gfs2: Check sb_bsize_shift after reading superblock

In the Linux kernel, the following vulnerability has been resolved: gfs2: Check sb_bsize_shift after reading superblock Fuzzers like to scribble over sb_bsize_shift but in reality it's very unlikely that this field would be corrupted on its own. Nevertheless it should be checked to avoid the possibility of messy mount errors due to bad calculations. It's always a fixed value based on the block size so we can just check that it's the expected value. Tested with: mkfs.gfs2 -O -p lock_nolock /dev/vdb for i in 0 -1 64 65 32 33; do gfs2_edit -p sb field sb_bsize_shift $i /dev/vdb mount /dev/vdb /mnt/test && umount /mnt/test done Before this patch we get a withdraw after [ 76.413681] gfs2: fsid=loop0.0: fatal: invalid metadata block [ 76.413681] bh = 19 (type: exp=5, found=4) [ 76.413681] function = gfs2_meta_buffer, file = fs/gfs2/meta_io.c, line = 492 and with UBSAN configured we also get complaints like [ 76.373395] UBSAN: shift-out-of-bounds in fs/gfs2/ops_fstype.c:295:19 [ 76.373815] shift exponent 4294967287 is too large for 64-bit type 'long unsigned int' After the patch, these complaints don't appear, mount fails immediately and we get an explanation in dmesg.

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Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于未检查sb_bsize_shift值，可能导致元数据损坏。

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