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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Marc Dionne <marc.dionne@auristor.com>,
        David Howells <dhowells@redhat.com>,
        Sasha Levin <sashal@kernel.org>, linux-afs@lists.infradead.org
Subject: [PATCH AUTOSEL 5.2 71/76] afs: Fix possible oops in afs_lookup trace event
Date:   Thu, 29 Aug 2019 14:13:06 -0400
Message-Id: <20190829181311.7562-71-sashal@kernel.org>
In-Reply-To: <20190829181311.7562-1-sashal@kernel.org>
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From: Marc Dionne <marc.dionne@auristor.com>

[ Upstream commit c4c613ff08d92e72bf64a65ec35a2c3aa1cfcd06 ]

The afs_lookup trace event can cause the following:

[  216.576777] BUG: kernel NULL pointer dereference, address: 000000000000023b
[  216.576803] #PF: supervisor read access in kernel mode
[  216.576813] #PF: error_code(0x0000) - not-present page
...
[  216.576913] RIP: 0010:trace_event_raw_event_afs_lookup+0x9e/0x1c0 [kafs]

If the inode from afs_do_lookup() is an error other than ENOENT, or if it
is ENOENT and afs_try_auto_mntpt() returns an error, the trace event will
try to dereference the error pointer as a valid pointer.

Use IS_ERR_OR_NULL to only pass a valid pointer for the trace, or NULL.

Ideally the trace would include the error value, but for now just avoid
the oops.

Fixes: 80548b03991f ("afs: Add more tracepoints")
Signed-off-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/afs/dir.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index da9563d62b327..c50cc3f6f4553 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -952,7 +952,8 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
 				 inode ? AFS_FS_I(inode) : NULL);
 	} else {
 		trace_afs_lookup(dvnode, &dentry->d_name,
-				 inode ? AFS_FS_I(inode) : NULL);
+				 IS_ERR_OR_NULL(inode) ? NULL
+				 : AFS_FS_I(inode));
 	}
 	return d;
 }
-- 
2.20.1