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tracing: Fix out of bounds write in get_trace_buf

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commit c1acb4ac1a892cf08d27efcb964ad281728b0545 upstream.

The nesting count of trace_printk allows for 4 levels of nesting. The
nesting counter starts at zero and is incremented before being used to
retrieve the current context's buffer. But the index to the buffer uses the
nesting counter after it was incremented, and not its original number,
which in needs to do.

Link: https://lkml.kernel.org/r/20201029161905.4269-1-hqjagain@gmail.com

Cc: stable@vger.kernel.org
Fixes: 3d9622c12c ("tracing: Add barrier to trace_printk() buffer nesting modification")
Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Qiujun Huang 2020-10-30 00:19:05 +08:00 committed by Greg Kroah-Hartman
parent 2de780dfbe
commit 7e4eeff7da
1 changed files with 1 additions and 1 deletions
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2
kernel/trace/trace.c
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@ -2819,7 +2819,7 @@ static char *get_trace_buf(void)
/* Interrupts must see nesting incremented before we use the buffer */ /* Interrupts must see nesting incremented before we use the buffer */
barrier(); barrier();
return &buffer->buffer[buffer->nesting][0]; return &buffer->buffer[buffer->nesting - 1][0];
} }
static void put_trace_buf(void) static void put_trace_buf(void)