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Groups > linux.kernel > #1235129
| From | Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH 3.10 20/56] fs: if a coredump already exists, unlink and recreate with O_EXCL |
| Date | 2015-09-29 16:10 +0200 |
| Message-ID | <qe3Lt-gh-15@gated-at.bofh.it> (permalink) |
| References | <qe3s5-85D-5@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
3.10-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jann Horn <jann@thejh.net>
commit fbb1816942c04429e85dbf4c1a080accc534299e upstream.
It was possible for an attacking user to trick root (or another user) into
writing his coredumps into an attacker-readable, pre-existing file using
rename() or link(), causing the disclosure of secret data from the victim
process' virtual memory. Depending on the configuration, it was also
possible to trick root into overwriting system files with coredumps. Fix
that issue by never writing coredumps into existing files.
Requirements for the attack:
- The attack only applies if the victim's process has a nonzero
RLIMIT_CORE and is dumpable.
- The attacker can trick the victim into coredumping into an
attacker-writable directory D, either because the core_pattern is
relative and the victim's cwd is attacker-writable or because an
absolute core_pattern pointing to a world-writable directory is used.
- The attacker has one of these:
A: on a system with protected_hardlinks=0:
execute access to a folder containing a victim-owned,
attacker-readable file on the same partition as D, and the
victim-owned file will be deleted before the main part of the attack
takes place. (In practice, there are lots of files that fulfill
this condition, e.g. entries in Debian's /var/lib/dpkg/info/.)
This does not apply to most Linux systems because most distros set
protected_hardlinks=1.
B: on a system with protected_hardlinks=1:
execute access to a folder containing a victim-owned,
attacker-readable and attacker-writable file on the same partition
as D, and the victim-owned file will be deleted before the main part
of the attack takes place.
(This seems to be uncommon.)
C: on any system, independent of protected_hardlinks:
write access to a non-sticky folder containing a victim-owned,
attacker-readable file on the same partition as D
(This seems to be uncommon.)
The basic idea is that the attacker moves the victim-owned file to where
he expects the victim process to dump its core. The victim process dumps
its core into the existing file, and the attacker reads the coredump from
it.
If the attacker can't move the file because he does not have write access
to the containing directory, he can instead link the file to a directory
he controls, then wait for the original link to the file to be deleted
(because the kernel checks that the link count of the corefile is 1).
A less reliable variant that requires D to be non-sticky works with link()
and does not require deletion of the original link: link() the file into
D, but then unlink() it directly before the kernel performs the link count
check.
On systems with protected_hardlinks=0, this variant allows an attacker to
not only gain information from coredumps, but also clobber existing,
victim-writable files with coredumps. (This could theoretically lead to a
privilege escalation.)
Signed-off-by: Jann Horn <jann@thejh.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/coredump.c | 38 ++++++++++++++++++++++++++++++++------
1 file changed, 32 insertions(+), 6 deletions(-)
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -491,10 +491,10 @@ void do_coredump(siginfo_t *siginfo)
const struct cred *old_cred;
struct cred *cred;
int retval = 0;
- int flag = 0;
int ispipe;
struct files_struct *displaced;
- bool need_nonrelative = false;
+ /* require nonrelative corefile path and be extra careful */
+ bool need_suid_safe = false;
bool core_dumped = false;
static atomic_t core_dump_count = ATOMIC_INIT(0);
struct coredump_params cprm = {
@@ -528,9 +528,8 @@ void do_coredump(siginfo_t *siginfo)
*/
if (__get_dumpable(cprm.mm_flags) == SUID_DUMP_ROOT) {
/* Setuid core dump mode */
- flag = O_EXCL; /* Stop rewrite attacks */
cred->fsuid = GLOBAL_ROOT_UID; /* Dump root private */
- need_nonrelative = true;
+ need_suid_safe = true;
}
retval = coredump_wait(siginfo->si_signo, &core_state);
@@ -611,7 +610,7 @@ void do_coredump(siginfo_t *siginfo)
if (cprm.limit < binfmt->min_coredump)
goto fail_unlock;
- if (need_nonrelative && cn.corename[0] != '/') {
+ if (need_suid_safe && cn.corename[0] != '/') {
printk(KERN_WARNING "Pid %d(%s) can only dump core "\
"to fully qualified path!\n",
task_tgid_vnr(current), current->comm);
@@ -619,8 +618,35 @@ void do_coredump(siginfo_t *siginfo)
goto fail_unlock;
}
+ /*
+ * Unlink the file if it exists unless this is a SUID
+ * binary - in that case, we're running around with root
+ * privs and don't want to unlink another user's coredump.
+ */
+ if (!need_suid_safe) {
+ mm_segment_t old_fs;
+
+ old_fs = get_fs();
+ set_fs(KERNEL_DS);
+ /*
+ * If it doesn't exist, that's fine. If there's some
+ * other problem, we'll catch it at the filp_open().
+ */
+ (void) sys_unlink((const char __user *)cn.corename);
+ set_fs(old_fs);
+ }
+
+ /*
+ * There is a race between unlinking and creating the
+ * file, but if that causes an EEXIST here, that's
+ * fine - another process raced with us while creating
+ * the corefile, and the other process won. To userspace,
+ * what matters is that at least one of the two processes
+ * writes its coredump successfully, not which one.
+ */
cprm.file = filp_open(cn.corename,
- O_CREAT | 2 | O_NOFOLLOW | O_LARGEFILE | flag,
+ O_CREAT | 2 | O_NOFOLLOW |
+ O_LARGEFILE | O_EXCL,
0600);
if (IS_ERR(cprm.file))
goto fail_unlock;
--
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[PATCH 3.10 00/56] 3.10.90-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 15:50 +0200
[PATCH 3.10 01/56] unshare: Unsharing a thread does not require unsharing a vm Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 15:50 +0200
[PATCH 3.10 04/56] mac80211: enable assoc check for mesh interfaces Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 15:50 +0200
[PATCH 3.10 02/56] rtlwifi: rtl8192cu: Add new device ID Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 15:50 +0200
[PATCH 3.10 17/56] NFS: nfs_set_pgio_error sometimes misses errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 15:50 +0200
[PATCH 3.10 25/56] IB/uverbs: reject invalid or unknown opcodes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 15:50 +0200
[PATCH 3.10 40/56] net: Fix skb csum races when peeking Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 43/56] isdn/gigaset: reset tty->receive_room when attaching ser_gigaset Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 55/56] vfs: Remove incorrect debugging WARN in prepend_path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 29/56] stmmac: fix check for phydev being open Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
Re: [PATCH 3.10 29/56] stmmac: fix check for phydev being open Sergei Shtylyov <sergei.shtylyov@cogentembedded.com> - 2015-09-30 13:30 +0200
[PATCH 3.10 49/56] ip6_gre: release cached dst on tunnel removal Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 27/56] IB/mlx4: Forbid using sysfs to change RoCE pkeys Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 31/56] sctp: fix ASCONF list handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 41/56] net: Fix skb_set_peeked use-after-free bug Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 32/56] vhost/scsi: potential memory corruption Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 30/56] hfs,hfsplus: cache pages correctly between bnode_create and bnode_free Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 35/56] net/tipc: initialize security state for new connection socket Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 52/56] net/ipv6: Correct PIM6 mrt_lock handling Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 50/56] usbnet: Get EVENT_NO_RUNTIME_PM bit before it is cleared Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 44/56] ipv6: lock socket in ip6_datagram_connect() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 42/56] bridge: mdb: fix double add notification Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 33/56] x86: bpf_jit: fix compilation of large bpf programs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 37/56] net: pktgen: fix race between pktgen_thread_worker() and kthread_stop() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 45/56] bonding: fix destruction of bond with devices different from arphrd_ether Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 53/56] sctp: fix race on protocol/netns initialization Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 47/56] netlink: dont hold mutex in rcu callback when releasing mmapd ring Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 36/56] bridge: mdb: zero out the local br_ip variable before use Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 48/56] rds: fix an integer overflow test in rds_info_getsockopt() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
Re: [PATCH 3.10 08/56] Input: synaptics - fix handling of disabling gesture mode Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2015-09-29 16:00 +0200
Re: [PATCH 3.10 08/56] Input: synaptics - fix handling of disabling gesture mode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:20 +0200
[PATCH 3.10 56/56] Revert "iio: bmg160: IIO_BUFFER and IIO_TRIGGERED_BUFFER are required" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 38/56] net: call rcu_read_lock early in process_backlog Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 54/56] fib_rules: fix fib rule dumps across multiple skbs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 46/56] inet: frags: fix defragmented packets IP header for af_packet Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 34/56] ipv6: Make MLD packets to only be processed locally Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 51/56] ipv6: fix exthdrs offload registration in out_rt path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 39/56] net: Clone skb before setting peeked flag Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:00 +0200
[PATCH 3.10 03/56] tg3: Fix temperature reporting Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 22/56] md/raid10: always set reshape_safe when initializing reshape_position. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 18/56] parisc: Filter out spurious interrupts in PA-RISC irq handler Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 13/56] Add radeon suspend/resume quirk for HP Compaq dc5750. Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 16/56] NFSv4: dont set SETATTR for O_RDONLY|O_EXCL Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 20/56] fs: if a coredump already exists, unlink and recreate with O_EXCL Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 08/56] Input: synaptics - fix handling of disabling gesture mode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 06/56] arm64: compat: fix vfp save/restore across signal handlers in big-endian Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 21/56] mmc: core: fix race condition in mmc_wait_data_done Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 24/56] hfs: fix B-tree corruption after insertion at position 0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 19/56] vmscan: fix increasing nr_isolated incurred by putback unevictable pages Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 12/56] powerpc/rtas: Introduce rtas_get_sensor_fast() for IRQ handlers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 11/56] powerpc/mm: Fix pte_pagesize_index() crash on 4K w/64K hash Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 07/56] arm64: head.S: initialise mdcr_el2 in el2_setup Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
[PATCH 3.10 26/56] IB/uverbs: Fix race between ib_uverbs_open and remove_one Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-29 16:10 +0200
Re: [PATCH 3.10 00/56] 3.10.90-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2015-09-29 19:00 +0200
Re: [PATCH 3.10 00/56] 3.10.90-stable review Guenter Roeck <linux@roeck-us.net> - 2015-09-29 23:20 +0200
Re: [PATCH 3.10 00/56] 3.10.90-stable review Sudip Mukherjee <sudipm.mukherjee@gmail.com> - 2015-09-30 07:50 +0200
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