[PATCH] mm: shmem: avoid overflowing in shmem_fallocate

[Sasha Levin]

"offset + len" has the potential of overflowing. Validate this user input
first to avoid undefined behaviour.

Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
 mm/shmem.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/shmem.c b/mm/shmem.c
index 185836b..5a0e344 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2098,6 +2098,9 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
 	}
 
 	/* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
+	error = -EOVERFLOW;
+	if ((u64)len + offset < (u64)len)
+		goto out;
 	error = inode_newsize_ok(inode, offset + len);
 	if (error)
 		goto out;
-- 
1.7.10.4

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