[PATCH] net: scm: Fix a possible sleep-in-atomic-context bug in scm_fp_copy()

[Jia-Ju Bai]

The kernel module may sleep with holding a spinlock.

The function call paths (from bottom to top) in Linux-4.16 are:

[FUNC] kmalloc(GFP_KERNEL)
net/core/scm.c, 85: kmalloc in scm_fp_copy
net/core/scm.c, 161: scm_fp_copy in __scm_send
./include/net/scm.h, 88: __scm_send in scm_send
net/unix/af_unix.c, 1600: scm_send in maybe_init_creds
net/unix/af_unix.c, 1983: maybe_init_creds in unix_stream_sendpage
net/unix/af_unix.c, 1973: spin_lock in unix_stream_sendpage

To fix this bug, GFP_KERNEL is replaced with GFP_ATOMIC.

This bug is found by my static analysis tool DSAC.

Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
---
 net/core/scm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/scm.c b/net/core/scm.c
index b1ff8a441748..49548f81c45b 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -82,7 +82,7 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
 
 	if (!fpl)
 	{
-		fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
+		fpl = kmalloc(sizeof(struct scm_fp_list), GFP_ATOMIC);
 		if (!fpl)
 			return -ENOMEM;
 		*fplp = fpl;
-- 
2.17.0