CVE-2022-50334

Summary

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

hugetlbfs: fix null-ptr-deref in hugetlbfs_parse_param()

Syzkaller reports a null-ptr-deref bug as follows:

KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:hugetlbfs_parse_param+0x1dd/0x8e0 fs/hugetlbfs/inode.c:1380 […] Call Trace: <TASK> vfs_parse_fs_param fs/fs_context.c:148 [inline] vfs_parse_fs_param+0x1f9/0x3c0 fs/fs_context.c:129 vfs_parse_fs_string+0xdb/0x170 fs/fs_context.c:191 generic_parse_monolithic+0x16f/0x1f0 fs/fs_context.c:231 do_new_mount fs/namespace.c:3036 [inline] path_mount+0x12de/0x1e20 fs/namespace.c:3370 do_mount fs/namespace.c:3383 [inline] __do_sys_mount fs/namespace.c:3591 [inline] __se_sys_mount fs/namespace.c:3568 [inline] __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd […] </TASK>

According to commit "vfs: parse: deal with zero length string value", kernel will set the param->string to null pointer in vfs_parse_fs_string() if fs string has zero length.

Yet the problem is that, hugetlbfs_parse_param() will dereference the param->string, without checking whether it is a null pointer. To be more specific, if hugetlbfs_parse_param() parses an illegal mount parameter, such as "size=,", kernel will constructs struct fs_parameter with null pointer in vfs_parse_fs_string(), then passes this struct fs_parameter to hugetlbfs_parse_param(), which triggers the above null-ptr-deref bug.

This patch solves it by adding sanity check on param->string in hugetlbfs_parse_param().

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/fa71639873518e3587632ae58e25e4a96b57fa90
• https://git.kernel.org/stable/c/dcd28191be9bbf307ba51a5b485773a55b0037c4
• https://git.kernel.org/stable/c/9a8862820cbf1f18dca4f3b4c289d88561b3a384
• https://git.kernel.org/stable/c/965e8f8ae0f642b5528f5a82b7bcaf15a659d5bd
• https://git.kernel.org/stable/c/f2207145693ae5697a7b59e2add4b92f9e5b0e3c
• https://git.kernel.org/stable/c/26215b7ee923b9251f7bb12c4e5f09dc465d35f2

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