jfs: jfs_dmap: Validate db_l2nbperpage while mounting

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: 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

References

• https://git.kernel.org/stable/c/8c1efe3f74a7864461b0dff281c5562154b4aa8e
• https://git.kernel.org/stable/c/ef5c205b6e6f8d1f18ef0b4a9832b1b5fa85f7f2
• https://git.kernel.org/stable/c/a4855aeb13e4ad1f23e16753b68212e180f7d848
• https://git.kernel.org/stable/c/47b7eaae08e8b2f25bdf37bc14d21be090bcb20f
• https://git.kernel.org/stable/c/de984faecddb900fa850af4df574a25b32bb93f5
• https://git.kernel.org/stable/c/c7feb54b113802d2aba98708769d3c33fb017254
• https://git.kernel.org/stable/c/2a03c4e683d33d17b667418eb717b13dda1fac6b
• https://git.kernel.org/stable/c/11509910c599cbd04585ec35a6d5e1a0053d84c1