jfs: jfs_dmap: Validate db_l2nbperpage while mounting

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commit 11509910c5 upstream.

In jfs_dmap.c at line 381, BLKTODMAP is used to get a logical block
number inside dbFree(). db_l2nbperpage, which is the log2 number of
blocks per page, is passed as an argument to BLKTODMAP which uses it
for shifting.

Syzbot reported a shift out-of-bounds crash because db_l2nbperpage is
too big. This happens because the large value is set without any
validation in dbMount() at line 181.

Thus, make sure that db_l2nbperpage is correct while mounting.

Max number of blocks per page = Page size / Min block size
=> log2(Max num_block per page) = log2(Page size / Min block size)
				= log2(Page size) - log2(Min block size)

=> Max db_l2nbperpage = L2PSIZE - L2MINBLOCKSIZE

Reported-and-tested-by: syzbot+d2cd27dcf8e04b232eb2@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?id=2a70a453331db32ed491f5cbb07e81bf2d225715
Cc: stable@vger.kernel.org
Suggested-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Siddh Raman Pant <code@siddh.me>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

This commit is contained in:

Siddh Raman Pant 2023-06-20 22:17:00 +05:30 • committed by Greg Kroah-Hartman

parent 9e54fd14bd

commit c7feb54b11

2 changed files with 8 additions and 0 deletions

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6

fs/jfs/jfs_dmap.c

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2

fs/jfs/jfs_filsys.h

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