Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1414539

[PATCH 3.14 18/23] ext4: address UBSAN warning in mb_find_order_for_block()

Show all headers | View raw

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicolai Stange <nicstange@gmail.com>

commit b5cb316cdf3a3f5f6125412b0f6065185240cfdc upstream.

Currently, in mb_find_order_for_block(), there's a loop like the following:

  while (order <= e4b->bd_blkbits + 1) {
    ...
    bb += 1 << (e4b->bd_blkbits - order);
  }

Note that the updated bb is used in the loop's next iteration only.

However, at the last iteration, that is at order == e4b->bd_blkbits + 1,
the shift count becomes negative (c.f. C99 6.5.7(3)) and UBSAN reports

  UBSAN: Undefined behaviour in fs/ext4/mballoc.c:1281:11
  shift exponent -1 is negative
  [...]
  Call Trace:
   [<ffffffff818c4d35>] dump_stack+0xbc/0x117
   [<ffffffff818c4c79>] ? _atomic_dec_and_lock+0x169/0x169
   [<ffffffff819411bb>] ubsan_epilogue+0xd/0x4e
   [<ffffffff81941cbc>] __ubsan_handle_shift_out_of_bounds+0x1fb/0x254
   [<ffffffff81941ac1>] ? __ubsan_handle_load_invalid_value+0x158/0x158
   [<ffffffff816e93a0>] ? ext4_mb_generate_from_pa+0x590/0x590
   [<ffffffff816502c8>] ? ext4_read_block_bitmap_nowait+0x598/0xe80
   [<ffffffff816e7b7e>] mb_find_order_for_block+0x1ce/0x240
   [...]

Unless compilers start to do some fancy transformations (which at least
GCC 6.0.0 doesn't currently do), the issue is of cosmetic nature only: the
such calculated value of bb is never used again.

Silence UBSAN by introducing another variable, bb_incr, holding the next
increment to apply to bb and adjust that one by right shifting it by one
position per loop iteration.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=114701
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=112161

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/ext4/mballoc.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1236,6 +1236,7 @@ static void ext4_mb_unload_buddy(struct
 static int mb_find_order_for_block(struct ext4_buddy *e4b, int block)
 {
 	int order = 1;
+	int bb_incr = 1 << (e4b->bd_blkbits - 1);
 	void *bb;
 
 	BUG_ON(e4b->bd_bitmap == e4b->bd_buddy);
@@ -1248,7 +1249,8 @@ static int mb_find_order_for_block(struc
 			/* this block is part of buddy of order 'order' */
 			return order;
 		}
-		bb += 1 << (e4b->bd_blkbits - order);
+		bb += bb_incr;
+		bb_incr >>= 1;
 		order++;
 	}
 	return 0;

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 3.14 00/23] 3.14.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-05 23:50 +0200
  [PATCH 3.14 07/23] aacraid: Fix for aac_command_thread hang Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-05 23:50 +0200
  [PATCH 3.14 11/23] pipe: Fix buffer offset after partially failed read Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-05 23:50 +0200
    Re: [PATCH 3.14 11/23] pipe: Fix buffer offset after partially failed  read Jiri Slaby <jslaby@suse.cz> - 2016-06-07 16:00 +0200
      Re: [PATCH 3.14 11/23] pipe: Fix buffer offset after partially  failed read Ben Hutchings <ben@decadent.org.uk> - 2016-06-07 16:50 +0200
  [PATCH 3.14 08/23] cpuidle: Indicate when a device has been unregistered Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-05 23:50 +0200
  [PATCH 3.14 03/23] MIPS: ath79: make bootconsole wait for both THRE and TEMT Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 05/23] ath5k: Change led pin configuration for compaq c700 laptop Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 19/23] ext4: silence UBSAN in ext4_mb_init() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 04/23] Input: uinput - handle compat ioctl for UI_SET_PHYS Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 13/23] xen/events: Dont move disabled irqs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 10/23] rtlwifi: Fix logic error in enter/exit power-save mode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 01/23] MIPS: math-emu: Fix jalr emulation when rd == $0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 06/23] aacraid: Relinquish CPU during timeout wait Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 17/23] ext4: fix hang when processing corrupted orphaned inode list Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 02/23] MIPS: Fix siginfo.h to use strict posix types Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 18/23] ext4: address UBSAN warning in mb_find_order_for_block() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  [PATCH 3.14 15/23] drm/gma500: Fix possible out of bounds read Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-06 01:10 +0200
  Re: [PATCH 3.14 00/23] 3.14.72-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2016-06-06 19:30 +0200
    Re: [PATCH 3.14 00/23] 3.14.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-06-08 02:30 +0200
  Re: [PATCH 3.14 00/23] 3.14.72-stable review Guenter Roeck <linux@roeck-us.net> - 2016-06-07 05:50 +0200

csiph-web