From: Roberto Sassu <roberto.sassu@xxxxxxxxxx> commit 935d44acf621aa0688fef8312dec3e5940f38f4e upstream. Ensure that file_seals is non-NULL before using it in the memfd_create() syscall. One situation in which memfd_file_seals_ptr() could return a NULL pointer when CONFIG_SHMEM=n, oopsing the kernel. Link: https://lkml.kernel.org/r/20230607132427.2867435-1-roberto.sassu@xxxxxxxxxxxxxxx Fixes: 47b9012ecdc7 ("shmem: add sealing support to hugetlb-backed memfd") Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> Cc: Marc-Andr Lureau <marcandre.lureau@xxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/memfd.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) --- a/mm/memfd.c +++ b/mm/memfd.c @@ -375,12 +375,15 @@ SYSCALL_DEFINE2(memfd_create, inode->i_mode &= ~0111; file_seals = memfd_file_seals_ptr(file); - *file_seals &= ~F_SEAL_SEAL; - *file_seals |= F_SEAL_EXEC; + if (file_seals) { + *file_seals &= ~F_SEAL_SEAL; + *file_seals |= F_SEAL_EXEC; + } } else if (flags & MFD_ALLOW_SEALING) { /* MFD_EXEC and MFD_ALLOW_SEALING are set */ file_seals = memfd_file_seals_ptr(file); - *file_seals &= ~F_SEAL_SEAL; + if (file_seals) + *file_seals &= ~F_SEAL_SEAL; } fd_install(fd, file);
