Hi Janusz, On 2024-07-18 at 10:55:16 +0200, Janusz Krzysztofik wrote: > 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> Reviewed-by: Kamil Konieczny <kamil.konieczny@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 c8c1079223..c251060341 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 >
