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[PATCH] apparmor: initialized returned struct aa_perms

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  [PATCH] apparmor: initialized returned struct aa_perms Arnd Bergmann <arnd@arndb.de> - 2017-09-15 22:00 +0200
    Re: [PATCH] apparmor: initialized returned struct aa_perms Seth Arnold <seth.arnold@canonical.com> - 2017-09-15 22:30 +0200
    Re: [PATCH] apparmor: initialized returned struct aa_perms Geert Uytterhoeven <geert@linux-m68k.org> - 2017-09-25 13:30 +0200
    Re: [PATCH] apparmor: initialized returned struct aa_perms John Johansen <john.johansen@canonical.com> - 2017-09-25 16:40 +0200

#1733062 — [PATCH] apparmor: initialized returned struct aa_perms

gcc-4.4 points out suspicious code in compute_mnt_perms, where
the aa_perms structure is only partially initialized before getting
returned:

security/apparmor/mount.c: In function 'compute_mnt_perms':
security/apparmor/mount.c:227: error: 'perms.prompt' is used uninitialized in this function
security/apparmor/mount.c:227: error: 'perms.hide' is used uninitialized in this function
security/apparmor/mount.c:227: error: 'perms.cond' is used uninitialized in this function
security/apparmor/mount.c:227: error: 'perms.complain' is used uninitialized in this function
security/apparmor/mount.c:227: error: 'perms.stop' is used uninitialized in this function
security/apparmor/mount.c:227: error: 'perms.deny' is used uninitialized in this function

Returning or assigning partially initialized structures is a bit tricky,
in particular it is explicitly allowed in c99 to assign a partially
intialized structure to another, as long as only members are read that
have been initialized earlier. Looking at what various compilers do here,
the version that produced the warning copied unintialized stack data,
while newer versions (and also clang) either set the other members to
zero or don't update the parts of the return buffer that are not modified
in the temporary structure, but they never warn about this.

In case of apparmor, it seems better to be a little safer and always
initialize the aa_perms structure. Most users already do that, this
changes the remaining ones, including the one instance that I got the
warning for.

Fixes: fa488437d0f9 ("apparmor: add mount mediation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 security/apparmor/file.c  |  8 +-------
 security/apparmor/lib.c   | 13 +++++--------
 security/apparmor/mount.c | 13 ++++++-------
 3 files changed, 12 insertions(+), 22 deletions(-)

diff --git a/security/apparmor/file.c b/security/apparmor/file.c
index db80221891c6..86d57e56fabe 100644
--- a/security/apparmor/file.c
+++ b/security/apparmor/file.c
@@ -227,18 +227,12 @@ static u32 map_old_perms(u32 old)
 struct aa_perms aa_compute_fperms(struct aa_dfa *dfa, unsigned int state,
 				  struct path_cond *cond)
 {
-	struct aa_perms perms;
-
 	/* FIXME: change over to new dfa format
 	 * currently file perms are encoded in the dfa, new format
 	 * splits the permissions from the dfa.  This mapping can be
 	 * done at profile load
 	 */
-	perms.deny = 0;
-	perms.kill = perms.stop = 0;
-	perms.complain = perms.cond = 0;
-	perms.hide = 0;
-	perms.prompt = 0;
+	struct aa_perms perms = { };
 
 	if (uid_eq(current_fsuid(), cond->uid)) {
 		perms.allow = map_old_perms(dfa_user_allow(dfa, state));
diff --git a/security/apparmor/lib.c b/security/apparmor/lib.c
index 8818621b5d95..6cbc06da964c 100644
--- a/security/apparmor/lib.c
+++ b/security/apparmor/lib.c
@@ -318,14 +318,11 @@ static u32 map_other(u32 x)
 void aa_compute_perms(struct aa_dfa *dfa, unsigned int state,
 		      struct aa_perms *perms)
 {
-	perms->deny = 0;
-	perms->kill = perms->stop = 0;
-	perms->complain = perms->cond = 0;
-	perms->hide = 0;
-	perms->prompt = 0;
-	perms->allow = dfa_user_allow(dfa, state);
-	perms->audit = dfa_user_audit(dfa, state);
-	perms->quiet = dfa_user_quiet(dfa, state);
+	*perms = (struct aa_perms) {
+		.allow = dfa_user_allow(dfa, state),
+		.audit = dfa_user_audit(dfa, state),
+		.quiet = dfa_user_quiet(dfa, state),
+	};
 
 	/* for v5 perm mapping in the policydb, the other set is used
 	 * to extend the general perm set
diff --git a/security/apparmor/mount.c b/security/apparmor/mount.c
index 82a64b58041d..ed9b4d0f9f7e 100644
--- a/security/apparmor/mount.c
+++ b/security/apparmor/mount.c
@@ -216,13 +216,12 @@ static unsigned int match_mnt_flags(struct aa_dfa *dfa, unsigned int state,
 static struct aa_perms compute_mnt_perms(struct aa_dfa *dfa,
 					   unsigned int state)
 {
-	struct aa_perms perms;
-
-	perms.kill = 0;
-	perms.allow = dfa_user_allow(dfa, state);
-	perms.audit = dfa_user_audit(dfa, state);
-	perms.quiet = dfa_user_quiet(dfa, state);
-	perms.xindex = dfa_user_xindex(dfa, state);
+	struct aa_perms perms = {
+		.allow = dfa_user_allow(dfa, state),
+		.audit = dfa_user_audit(dfa, state),
+		.quiet = dfa_user_quiet(dfa, state),
+		.xindex = dfa_user_xindex(dfa, state),
+	};
 
 	return perms;
 }
-- 
2.9.0

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#1733076

[Multipart message — attachments visible in raw view] — view raw

On Fri, Sep 15, 2017 at 09:55:46PM +0200, Arnd Bergmann wrote:
> gcc-4.4 points out suspicious code in compute_mnt_perms, where
> the aa_perms structure is only partially initialized before getting
> returned:
> 
> security/apparmor/mount.c: In function 'compute_mnt_perms':
> security/apparmor/mount.c:227: error: 'perms.prompt' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.hide' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.cond' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.complain' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.stop' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.deny' is used uninitialized in this function
> 
> Returning or assigning partially initialized structures is a bit tricky,
> in particular it is explicitly allowed in c99 to assign a partially
> intialized structure to another, as long as only members are read that
> have been initialized earlier. Looking at what various compilers do here,
> the version that produced the warning copied unintialized stack data,
> while newer versions (and also clang) either set the other members to
> zero or don't update the parts of the return buffer that are not modified
> in the temporary structure, but they never warn about this.
> 
> In case of apparmor, it seems better to be a little safer and always
> initialize the aa_perms structure. Most users already do that, this
> changes the remaining ones, including the one instance that I got the
> warning for.
> 
> Fixes: fa488437d0f9 ("apparmor: add mount mediation")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Reviewed-by: Seth Arnold <seth.arnold@canonical.com>

Thanks

> ---
>  security/apparmor/file.c  |  8 +-------
>  security/apparmor/lib.c   | 13 +++++--------
>  security/apparmor/mount.c | 13 ++++++-------
>  3 files changed, 12 insertions(+), 22 deletions(-)
> 
> diff --git a/security/apparmor/file.c b/security/apparmor/file.c
> index db80221891c6..86d57e56fabe 100644
> --- a/security/apparmor/file.c
> +++ b/security/apparmor/file.c
> @@ -227,18 +227,12 @@ static u32 map_old_perms(u32 old)
>  struct aa_perms aa_compute_fperms(struct aa_dfa *dfa, unsigned int state,
>  				  struct path_cond *cond)
>  {
> -	struct aa_perms perms;
> -
>  	/* FIXME: change over to new dfa format
>  	 * currently file perms are encoded in the dfa, new format
>  	 * splits the permissions from the dfa.  This mapping can be
>  	 * done at profile load
>  	 */
> -	perms.deny = 0;
> -	perms.kill = perms.stop = 0;
> -	perms.complain = perms.cond = 0;
> -	perms.hide = 0;
> -	perms.prompt = 0;
> +	struct aa_perms perms = { };
>  
>  	if (uid_eq(current_fsuid(), cond->uid)) {
>  		perms.allow = map_old_perms(dfa_user_allow(dfa, state));
> diff --git a/security/apparmor/lib.c b/security/apparmor/lib.c
> index 8818621b5d95..6cbc06da964c 100644
> --- a/security/apparmor/lib.c
> +++ b/security/apparmor/lib.c
> @@ -318,14 +318,11 @@ static u32 map_other(u32 x)
>  void aa_compute_perms(struct aa_dfa *dfa, unsigned int state,
>  		      struct aa_perms *perms)
>  {
> -	perms->deny = 0;
> -	perms->kill = perms->stop = 0;
> -	perms->complain = perms->cond = 0;
> -	perms->hide = 0;
> -	perms->prompt = 0;
> -	perms->allow = dfa_user_allow(dfa, state);
> -	perms->audit = dfa_user_audit(dfa, state);
> -	perms->quiet = dfa_user_quiet(dfa, state);
> +	*perms = (struct aa_perms) {
> +		.allow = dfa_user_allow(dfa, state),
> +		.audit = dfa_user_audit(dfa, state),
> +		.quiet = dfa_user_quiet(dfa, state),
> +	};
>  
>  	/* for v5 perm mapping in the policydb, the other set is used
>  	 * to extend the general perm set
> diff --git a/security/apparmor/mount.c b/security/apparmor/mount.c
> index 82a64b58041d..ed9b4d0f9f7e 100644
> --- a/security/apparmor/mount.c
> +++ b/security/apparmor/mount.c
> @@ -216,13 +216,12 @@ static unsigned int match_mnt_flags(struct aa_dfa *dfa, unsigned int state,
>  static struct aa_perms compute_mnt_perms(struct aa_dfa *dfa,
>  					   unsigned int state)
>  {
> -	struct aa_perms perms;
> -
> -	perms.kill = 0;
> -	perms.allow = dfa_user_allow(dfa, state);
> -	perms.audit = dfa_user_audit(dfa, state);
> -	perms.quiet = dfa_user_quiet(dfa, state);
> -	perms.xindex = dfa_user_xindex(dfa, state);
> +	struct aa_perms perms = {
> +		.allow = dfa_user_allow(dfa, state),
> +		.audit = dfa_user_audit(dfa, state),
> +		.quiet = dfa_user_quiet(dfa, state),
> +		.xindex = dfa_user_xindex(dfa, state),
> +	};
>  
>  	return perms;
>  }

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#1738949

On Fri, Sep 15, 2017 at 9:55 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> gcc-4.4 points out suspicious code in compute_mnt_perms, where
> the aa_perms structure is only partially initialized before getting
> returned:
>
> security/apparmor/mount.c: In function 'compute_mnt_perms':
> security/apparmor/mount.c:227: error: 'perms.prompt' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.hide' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.cond' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.complain' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.stop' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.deny' is used uninitialized in this function
>
> Returning or assigning partially initialized structures is a bit tricky,
> in particular it is explicitly allowed in c99 to assign a partially
> intialized structure to another, as long as only members are read that
> have been initialized earlier. Looking at what various compilers do here,
> the version that produced the warning copied unintialized stack data,
> while newer versions (and also clang) either set the other members to
> zero or don't update the parts of the return buffer that are not modified
> in the temporary structure, but they never warn about this.
>
> In case of apparmor, it seems better to be a little safer and always
> initialize the aa_perms structure. Most users already do that, this
> changes the remaining ones, including the one instance that I got the
> warning for.
>
> Fixes: fa488437d0f9 ("apparmor: add mount mediation")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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#1739093

On 09/15/2017 03:55 PM, Arnd Bergmann wrote:
> gcc-4.4 points out suspicious code in compute_mnt_perms, where
> the aa_perms structure is only partially initialized before getting
> returned:
> 
> security/apparmor/mount.c: In function 'compute_mnt_perms':
> security/apparmor/mount.c:227: error: 'perms.prompt' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.hide' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.cond' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.complain' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.stop' is used uninitialized in this function
> security/apparmor/mount.c:227: error: 'perms.deny' is used uninitialized in this function
> 
> Returning or assigning partially initialized structures is a bit tricky,
> in particular it is explicitly allowed in c99 to assign a partially
> intialized structure to another, as long as only members are read that
> have been initialized earlier. Looking at what various compilers do here,
> the version that produced the warning copied unintialized stack data,
> while newer versions (and also clang) either set the other members to
> zero or don't update the parts of the return buffer that are not modified
> in the temporary structure, but they never warn about this.
> 
> In case of apparmor, it seems better to be a little safer and always
> initialize the aa_perms structure. Most users already do that, this
> changes the remaining ones, including the one instance that I got the
> warning for.
> 
> Fixes: fa488437d0f9 ("apparmor: add mount mediation")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

I've pulled this into apparmor-next


> ---
>  security/apparmor/file.c  |  8 +-------
>  security/apparmor/lib.c   | 13 +++++--------
>  security/apparmor/mount.c | 13 ++++++-------
>  3 files changed, 12 insertions(+), 22 deletions(-)
> 
> diff --git a/security/apparmor/file.c b/security/apparmor/file.c
> index db80221891c6..86d57e56fabe 100644
> --- a/security/apparmor/file.c
> +++ b/security/apparmor/file.c
> @@ -227,18 +227,12 @@ static u32 map_old_perms(u32 old)
>  struct aa_perms aa_compute_fperms(struct aa_dfa *dfa, unsigned int state,
>  				  struct path_cond *cond)
>  {
> -	struct aa_perms perms;
> -
>  	/* FIXME: change over to new dfa format
>  	 * currently file perms are encoded in the dfa, new format
>  	 * splits the permissions from the dfa.  This mapping can be
>  	 * done at profile load
>  	 */
> -	perms.deny = 0;
> -	perms.kill = perms.stop = 0;
> -	perms.complain = perms.cond = 0;
> -	perms.hide = 0;
> -	perms.prompt = 0;
> +	struct aa_perms perms = { };
>  
>  	if (uid_eq(current_fsuid(), cond->uid)) {
>  		perms.allow = map_old_perms(dfa_user_allow(dfa, state));
> diff --git a/security/apparmor/lib.c b/security/apparmor/lib.c
> index 8818621b5d95..6cbc06da964c 100644
> --- a/security/apparmor/lib.c
> +++ b/security/apparmor/lib.c
> @@ -318,14 +318,11 @@ static u32 map_other(u32 x)
>  void aa_compute_perms(struct aa_dfa *dfa, unsigned int state,
>  		      struct aa_perms *perms)
>  {
> -	perms->deny = 0;
> -	perms->kill = perms->stop = 0;
> -	perms->complain = perms->cond = 0;
> -	perms->hide = 0;
> -	perms->prompt = 0;
> -	perms->allow = dfa_user_allow(dfa, state);
> -	perms->audit = dfa_user_audit(dfa, state);
> -	perms->quiet = dfa_user_quiet(dfa, state);
> +	*perms = (struct aa_perms) {
> +		.allow = dfa_user_allow(dfa, state),
> +		.audit = dfa_user_audit(dfa, state),
> +		.quiet = dfa_user_quiet(dfa, state),
> +	};
>  
>  	/* for v5 perm mapping in the policydb, the other set is used
>  	 * to extend the general perm set
> diff --git a/security/apparmor/mount.c b/security/apparmor/mount.c
> index 82a64b58041d..ed9b4d0f9f7e 100644
> --- a/security/apparmor/mount.c
> +++ b/security/apparmor/mount.c
> @@ -216,13 +216,12 @@ static unsigned int match_mnt_flags(struct aa_dfa *dfa, unsigned int state,
>  static struct aa_perms compute_mnt_perms(struct aa_dfa *dfa,
>  					   unsigned int state)
>  {
> -	struct aa_perms perms;
> -
> -	perms.kill = 0;
> -	perms.allow = dfa_user_allow(dfa, state);
> -	perms.audit = dfa_user_audit(dfa, state);
> -	perms.quiet = dfa_user_quiet(dfa, state);
> -	perms.xindex = dfa_user_xindex(dfa, state);
> +	struct aa_perms perms = {
> +		.allow = dfa_user_allow(dfa, state),
> +		.audit = dfa_user_audit(dfa, state),
> +		.quiet = dfa_user_quiet(dfa, state),
> +		.xindex = dfa_user_xindex(dfa, state),
> +	};
>  
>  	return perms;
>  }
> 

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