drm/radeon: fix a rare case of double kfree

commit 1da80cfa8727abf404fcee44d04743febea54069 upstream.

If one (but not both) allocations of p->chunks[].kpage[]
in radeon_cs_parser_init fail, the error path will free
the successfully allocated page, but leave a stale pointer
value in the kpage[] field. This will later cause a
double-free when radeon_cs_parser_fini is called.
This patch fixes the issue by forcing both pointers to NULL
after kfree in the error path.

The circumstances under which the problem happens are very
rare. The card must be AGP and the system must run out of
kmalloc area just at the right time so that one allocation
succeeds, while the other fails.

Signed-off-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Cc: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[bwh: Backported to 3.2: s/p->chunk_ib_idx/i/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/gpu/drm/radeon/radeon_cs.c b/drivers/gpu/drm/radeon/radeon_cs.c
index 29afd71e0840a0b9995b5e30027577adeec45b92..1f32557a4d840f7a5758be463950f88ee941c854 100644 (file)
--- a/drivers/gpu/drm/radeon/radeon_cs.c
+++ b/drivers/gpu/drm/radeon/radeon_cs.c
@@ -168,6 +168,8 @@ int radeon_cs_parser_init(struct radeon_cs_parser *p, void *data)
                        if (p->chunks[i].kpage[0] == NULL || p->chunks[i].kpage[1] == NULL) {
                                kfree(p->chunks[i].kpage[0]);
                                kfree(p->chunks[i].kpage[1]);
+                               p->chunks[i].kpage[0] = NULL;
+                               p->chunks[i].kpage[1] = NULL;
                                return -ENOMEM;
                        }
                        p->chunks[i].kpage_idx[0] = -1;