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tracing/synthetic: Fix races on freeing last_cmd
commit4ccf11c4e8
upstream. Currently, the "last_cmd" variable can be accessed by multiple processes asynchronously when multiple users manipulate synthetic_events node at the same time, it could lead to use-after-free or double-free. This patch add "lastcmd_mutex" to prevent "last_cmd" from being accessed asynchronously. ================================================================ It's easy to reproduce in the KASAN environment by running the two scripts below in different shells. script 1: while : do echo -n -e '\x88' > /sys/kernel/tracing/synthetic_events done script 2: while : do echo -n -e '\xb0' > /sys/kernel/tracing/synthetic_events done ================================================================ double-free scenario: process A process B ------------------- --------------- 1.kstrdup last_cmd 2.free last_cmd 3.free last_cmd(double-free) ================================================================ use-after-free scenario: process A process B ------------------- --------------- 1.kstrdup last_cmd 2.free last_cmd 3.tracing_log_err(use-after-free) ================================================================ Appendix 1. KASAN report double-free: BUG: KASAN: double-free in kfree+0xdc/0x1d4 Free of addr ***** by task sh/4879 Call trace: ... kfree+0xdc/0x1d4 create_or_delete_synth_event+0x60/0x1e8 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ... Allocated by task 4879: ... kstrdup+0x5c/0x98 create_or_delete_synth_event+0x6c/0x1e8 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ... Freed by task 5464: ... kfree+0xdc/0x1d4 create_or_delete_synth_event+0x60/0x1e8 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ... ================================================================ Appendix 2. KASAN report use-after-free: BUG: KASAN: use-after-free in strlen+0x5c/0x7c Read of size 1 at addr ***** by task sh/5483 sh: CPU: 7 PID: 5483 Comm: sh ... __asan_report_load1_noabort+0x34/0x44 strlen+0x5c/0x7c tracing_log_err+0x60/0x444 create_or_delete_synth_event+0xc4/0x204 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ... Allocated by task 5483: ... kstrdup+0x5c/0x98 create_or_delete_synth_event+0x80/0x204 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ... Freed by task 5480: ... kfree+0xdc/0x1d4 create_or_delete_synth_event+0x74/0x204 trace_parse_run_command+0x2bc/0x4b8 synth_events_write+0x20/0x30 vfs_write+0x200/0x830 ... Link: https://lore.kernel.org/linux-trace-kernel/20230321110444.1587-1-Tze-nan.Wu@mediatek.com Fixes:27c888da98
("tracing: Remove size restriction on synthetic event cmd error logging") Cc: stable@vger.kernel.org Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Matthias Brugger <matthias.bgg@gmail.com> Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> Cc: "Tom Zanussi" <zanussi@kernel.org> Signed-off-by: Tze-nan Wu <Tze-nan.Wu@mediatek.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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parent
101e8e6bba
commit
9fe183f659
1 changed files with 16 additions and 5 deletions
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@ -44,14 +44,21 @@ enum { ERRORS };
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static const char *err_text[] = { ERRORS };
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DEFINE_MUTEX(lastcmd_mutex);
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static char *last_cmd;
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static int errpos(const char *str)
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{
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if (!str || !last_cmd)
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return 0;
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int ret = 0;
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return err_pos(last_cmd, str);
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mutex_lock(&lastcmd_mutex);
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if (!str || !last_cmd)
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goto out;
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ret = err_pos(last_cmd, str);
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out:
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mutex_unlock(&lastcmd_mutex);
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return ret;
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}
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static void last_cmd_set(const char *str)
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@ -59,18 +66,22 @@ static void last_cmd_set(const char *str)
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if (!str)
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return;
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mutex_lock(&lastcmd_mutex);
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kfree(last_cmd);
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last_cmd = kstrdup(str, GFP_KERNEL);
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mutex_unlock(&lastcmd_mutex);
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}
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static void synth_err(u8 err_type, u16 err_pos)
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{
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mutex_lock(&lastcmd_mutex);
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if (!last_cmd)
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return;
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goto out;
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tracing_log_err(NULL, "synthetic_events", last_cmd, err_text,
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err_type, err_pos);
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out:
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mutex_unlock(&lastcmd_mutex);
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}
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static int create_synth_event(const char *raw_command);
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