[PATCH v2] mm/fadvise: validate offset in generic_fadvise

[klourencodev@gmail.com]

From: Kevin Lourenco <klourencodev@gmail.com>

When converted to (u64) for page calculations, a negative offset can
produce extremely large page indices. This may lead to issues in certain
advice modes (excessive readahead or cache invalidation).

Reject negative offsets with -EINVAL for consistent argument validation
and to avoid silent misbehavior.

POSIX and the man page do not clearly define behavior for negative
offset/len. FreeBSD rejects negative offsets as well, so failing with
-EINVAL is consistent with existing practice. The man page can be
updated separately to document the Linux behavior.

Signed-off-by: Kevin Lourenco <klourencodev@gmail.com>
---
 mm/fadvise.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/fadvise.c b/mm/fadvise.c
index 67028e30aa91..b63fe21416ff 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -43,7 +43,7 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 		return -ESPIPE;
 
 	mapping = file->f_mapping;
-	if (!mapping || len < 0)
+	if (!mapping || len < 0 || offset < 0)
 		return -EINVAL;
 
 	bdi = inode_to_bdi(mapping->host);
-- 
2.52.0