[PATCH 3.12 054/122] pstore: Fix NULL pointer fault if get NULL prz in ramoops_get_next_prz

[Jiri Slaby]

From: Liu ShuoX <shuox.liu@xxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit b0aa931fb84431394d995472d0af2a6c2b61064d upstream.

ramoops_get_next_prz get the prz according the paramters. If it get a
uninitialized prz, access its members by following persistent_ram_old_size(prz)
will cause a NULL pointer crash.
Ex: if ftrace_size is 0, fprz will be NULL.

Fix it by return NULL in advance.

Signed-off-by: Liu ShuoX <shuox.liu@xxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
Cc: HuKeping <hukeping@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 fs/pstore/ram.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 808435a9e2e1..fe68d8ac4d3d 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -125,6 +125,8 @@ ramoops_get_next_prz(struct persistent_ram_zone *przs[], uint *c, uint max,
 		return NULL;
 
 	prz = przs[i];
+	if (!prz)
+		return NULL;
 
 	/* Update old/shadowed buffer. */
 	if (update)
-- 
2.2.2

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