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* [PATCH] statfs: fix potential Spectre v1
@ 2018-08-15 13:36 Gustavo A. R. Silva
  0 siblings, 0 replies; only message in thread
From: Gustavo A. R. Silva @ 2018-08-15 13:36 UTC (permalink / raw)
  To: Alexander Viro; +Cc: linux-fsdevel, linux-kernel, Gustavo A. R. Silva

user_params.request is indirectly controlled by user-space, hence leading
to a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

fs/statfs.c:908 __do_sys_fsinfo() warn: potential spectre issue
'fsinfo_buffer_sizes' [r]

Fix this by sanitizing user_params.request before using it to index

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].


Signed-off-by: Gustavo A. R. Silva <>
 fs/statfs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/statfs.c b/fs/statfs.c
index f714f05..d74a60a 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -11,6 +11,7 @@
 #include <linux/compat.h>
 #include <linux/fsinfo.h>
 #include <linux/fs_parser.h>
+#include <linux/nospec.h>
 #include "internal.h"
 static int flags_by_mnt(int mnt_flags)
@@ -886,6 +887,8 @@ SYSCALL_DEFINE5(fsinfo,
 			return -EINVAL;
 		if (user_params.request >= FSINFO_ATTR__NR)
 			return -EOPNOTSUPP;
+		user_params.request = array_index_nospec(user_params.request,
+							 FSINFO_ATTR__NR);
 		params.at_flags = user_params.at_flags;
 		params.request = user_params.request;
 		params.Nth = user_params.Nth;

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