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  1. 11 1月, 2012 1 次提交
    • X
      ext4: fix undefined behavior in ext4_fill_flex_info() · d50f2ab6
      由 Xi Wang 提交于 
      Commit 503358ae ("ext4: avoid divide by
zero when trying to mount a corrupted file system") fixes CVE-2009-4307
by performing a sanity check on s_log_groups_per_flex, since it can be
set to a bogus value by an attacker.

	sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;
	groups_per_flex = 1 << sbi->s_log_groups_per_flex;

	if (groups_per_flex < 2) { ... }

This patch fixes two potential issues in the previous commit.

1) The sanity check might only work on architectures like PowerPC.
On x86, 5 bits are used for the shifting amount.  That means, given a
large s_log_groups_per_flex value like 36, groups_per_flex = 1 << 36
is essentially 1 << 4 = 16, rather than 0.  This will bypass the check,
leaving s_log_groups_per_flex and groups_per_flex inconsistent.

2) The sanity check relies on undefined behavior, i.e., oversized shift.
A standard-confirming C compiler could rewrite the check in unexpected
ways.  Consider the following equivalent form, assuming groups_per_flex
is unsigned for simplicity.

	groups_per_flex = 1 << sbi->s_log_groups_per_flex;
	if (groups_per_flex == 0 || groups_per_flex == 1) {

We compile the code snippet using Clang 3.0 and GCC 4.6.  Clang will
completely optimize away the check groups_per_flex == 0, leaving the
patched code as vulnerable as the original.  GCC keeps the check, but
there is no guarantee that future versions will do the same.
Signed-off-by: NXi Wang <xi.wang@gmail.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
      d50f2ab6
  3. 05 1月, 2012 9 次提交
  5. 04 1月, 2012 9 次提交
  7. 29 12月, 2011 7 次提交
  9. 22 12月, 2011 1 次提交
    • T
      ext4: remove unneeded file_remove_suid() from ext4_ioctl() · 22cdfca5
      由 Theodore Ts'o 提交于 
      In the code to support EXT4_IOC_MOVE_EXT, ext4_ioctl calls
file_remove_suid() after the call to ext4_move_extents() if any
extents has been moved.  There are at least three things wrong with
this.  First, file_remove_suid() should be called with i_mutex down,
which is not here.  Second, it should be called before the donor file
has been modified, to avoid a potential race condition.  Third, and
most importantly, it's pointless, because ext4_file_extents() already
checks if the donor file has the setuid or setgid bit set, and will
return an error in that case.  So the first two objections don't
really matter, since file_remove_suid() will never need to modify the
inode in any case.
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
      22cdfca5
  11. 19 12月, 2011 5 次提交
  13. 17 12月, 2011 8 次提交