6.6-stable review patch. If anyone has any objections, please let me know.
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From: Namhyung Kim namhyung@kernel.org
[ Upstream commit 1fdf938168c4d26fa279d4f204768690d1f9c4ae ]
Currently perf aborts when it finds an invalid command. I guess it depends on the environment as I have some custom commands in the path.
$ perf bad-command perf: 'bad-command' is not a perf-command. See 'perf --help'. Aborted (core dumped)
It's because the exclude_cmds() in libsubcmd has a use-after-free when it removes some entries. After copying one to another entry, it keeps the pointer in the both position. And the next copy operation will free the later one but it's the same entry in the previous one.
For example, let's say cmds = { A, B, C, D, E } and excludes = { B, E }.
ci cj ei cmds-name excludes -----------+-------------------- 0 0 0 | A B : cmp < 0, ci == cj 1 1 0 | B B : cmp == 0 2 1 1 | C E : cmp < 0, ci != cj
At this point, it frees cmds->names[1] and cmds->names[1] is assigned to cmds->names[2].
3 2 1 | D E : cmp < 0, ci != cj
Now it frees cmds->names[2] but it's the same as cmds->names[1]. So accessing cmds->names[1] will be invalid.
This makes the subcmd tests succeed.
$ perf test subcmd 69: libsubcmd help tests : 69.1: Load subcmd names : Ok 69.2: Uniquify subcmd names : Ok 69.3: Exclude duplicate subcmd names : Ok
Fixes: 4b96679170c6 ("libsubcmd: Avoid SEGV/use-after-free when commands aren't excluded") Reviewed-by: Ian Rogers irogers@google.com Link: https://lore.kernel.org/r/20250701201027.1171561-3-namhyung@kernel.org Signed-off-by: Namhyung Kim namhyung@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/subcmd/help.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/tools/lib/subcmd/help.c b/tools/lib/subcmd/help.c index 8561b0f01a24..9ef569492560 100644 --- a/tools/lib/subcmd/help.c +++ b/tools/lib/subcmd/help.c @@ -9,6 +9,7 @@ #include <sys/stat.h> #include <unistd.h> #include <dirent.h> +#include <assert.h> #include "subcmd-util.h" #include "help.h" #include "exec-cmd.h" @@ -82,10 +83,11 @@ void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes) ci++; cj++; } else { - zfree(&cmds->names[cj]); - cmds->names[cj++] = cmds->names[ci++]; + cmds->names[cj++] = cmds->names[ci]; + cmds->names[ci++] = NULL; } } else if (cmp == 0) { + zfree(&cmds->names[ci]); ci++; ei++; } else if (cmp > 0) { @@ -94,12 +96,12 @@ void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes) } if (ci != cj) { while (ci < cmds->cnt) { - zfree(&cmds->names[cj]); - cmds->names[cj++] = cmds->names[ci++]; + cmds->names[cj++] = cmds->names[ci]; + cmds->names[ci++] = NULL; } } for (ci = cj; ci < cmds->cnt; ci++) - zfree(&cmds->names[ci]); + assert(cmds->names[ci] == NULL); cmds->cnt = cj; }