When looking for a primary counterpart of a render device, we compare "device" links of both nodes. If those links point to the same device then we know we've found the correct primary node. However, readlinkat() function we use doesn't explicitly terminate read in strings with null characters, and then the comparison occasionally fails. Process the second (potential primary counterpart) node only if its "device" link is of the same length as that of the render node, and limit the number of compared characters to that length. Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/6268 Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@xxxxxxxxxxxxxxx> --- lib/i915/gem_engine_topology.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/lib/i915/gem_engine_topology.c b/lib/i915/gem_engine_topology.c index d14190f253..777fbca938 100644 --- a/lib/i915/gem_engine_topology.c +++ b/lib/i915/gem_engine_topology.c @@ -467,7 +467,8 @@ static int __open_primary(int dir) if (minor < 64) return dir; - if (igt_debug_on(readlinkat(dir, "device", target, sizeof(target)) < 0)) + len = readlinkat(dir, "device", target, sizeof(target)); + if (igt_debug_on(len <= 0)) return dir; close(dir); @@ -477,8 +478,8 @@ static int __open_primary(int dir) if (dir < 0) continue; - if (readlinkat(dir, "device", device, sizeof(device)) > 0 && - !strcmp(device, target)) + if (readlinkat(dir, "device", device, sizeof(device)) == len && + !strncmp(device, target, len) break; close(dir); -- 2.45.2
