Revision 3e536e222f2930534c252c1cc7ae799c725c5ff9 authored by Snild Dolkow on 26 July 2018, 07:15:39 UTC, committed by Steven Rostedt (VMware) on 26 July 2018, 13:59:33 UTC
There is a window for racing when printing directly to task->comm, allowing other threads to see a non-terminated string. The vsnprintf function fills the buffer, counts the truncated chars, then finally writes the \0 at the end. creator other vsnprintf: fill (not terminated) count the rest trace_sched_waking(p): ... memcpy(comm, p->comm, TASK_COMM_LEN) write \0 The consequences depend on how 'other' uses the string. In our case, it was copied into the tracing system's saved cmdlines, a buffer of adjacent TASK_COMM_LEN-byte buffers (note the 'n' where 0 should be): crash-arm64> x/1024s savedcmd->saved_cmdlines | grep 'evenk' 0xffffffd5b3818640: "irq/497-pwr_evenkworker/u16:12" ...and a strcpy out of there would cause stack corruption: [224761.522292] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: ffffff9bf9783c78 crash-arm64> kbt | grep 'comm\|trace_print_context' #6 0xffffff9bf9783c78 in trace_print_context+0x18c(+396) comm (char [16]) = "irq/497-pwr_even" crash-arm64> rd 0xffffffd4d0e17d14 8 ffffffd4d0e17d14: 2f71726900000000 5f7277702d373934 ....irq/497-pwr_ ffffffd4d0e17d24: 726f776b6e657665 3a3631752f72656b evenkworker/u16: ffffffd4d0e17d34: f9780248ff003231 cede60e0ffffff9b 12..H.x......`.. ffffffd4d0e17d44: cede60c8ffffffd4 00000fffffffffd4 .....`.......... The workaround in e09e28671 (use strlcpy in __trace_find_cmdline) was likely needed because of this same bug. Solved by vsnprintf:ing to a local buffer, then using set_task_comm(). This way, there won't be a window where comm is not terminated. Link: http://lkml.kernel.org/r/20180726071539.188015-1-snild@sony.com Cc: stable@vger.kernel.org Fixes: bc0c38d139ec7 ("ftrace: latency tracer infrastructure") Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Snild Dolkow <snild@sony.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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