ext4: add validity checks for bitmap block numbers
commit
7dac4a1726a9c64a517d595c40e95e2d0d135f6f upstream.
An privileged attacker can cause a crash by mounting a crafted ext4
image which triggers a out-of-bounds read in the function
ext4_valid_block_bitmap() in fs/ext4/balloc.c.
This issue has been assigned CVE-2018-1093.
BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=199181
BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1560782
Reported-by: Wen Xu <wen.xu@gatech.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.2:
- In ext4_valid_block_bitmap(), goto err_out on error
- In ext4_read_{block,inode}_bitmap(), return NULL on error
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>