jfs: jfs_dmap: Validate db_l2nbperpage while mounting

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: [email protected]
Closes: https://syzkaller.appspot.com/bug?id=2a70a453331db32ed491f5cbb07e81bf2d225715
Cc: [email protected]
Suggested-by: Dave Kleikamp <[email protected]>
Signed-off-by: Siddh Raman Pant <[email protected]>
Signed-off-by: Dave Kleikamp <[email protected]>

0 files changed, 0 insertions, 0 deletions