Linus (aka Greg),
It was reported that trace_printk() was not reporting properly values that came after a dereference pointer.
trace_printk() utilizes vbin_printf() and bstr_printf() to keep the overhead of tracing down. vbin_printf() does not do any conversions and just stors the string format and the raw arguments into the buffer. bstr_printf() is used to read the buffer and does the conversions to complete the printf() output.
This can be troublesome with dereferenced pointers because the reference may be different from the time vbin_printf() is called to the time bstr_printf() is called. To fix this, a prior commit changed vbin_printf() to convert dereferenced pointers into strings and load the converted string into the buffer. But the change to bstr_printf() had an off-by-one error and didn't account for the nul character at the end of the string and this corrupted the rest of the values in the format that came after a dereferenced pointer.
Please pull the latest trace-v4.19-rc5 tree, which can be found at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git trace-v4.19-rc5
Tag SHA1: b5fc80d980ae316323e88c165084deef39afd168 Head SHA1: 62165600ae73ebd76e2d9b992b36360408d570d8
Steven Rostedt (VMware) (1): vsprintf: Fix off-by-one bug in bstr_printf() processing dereferenced pointers
---- lib/vsprintf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --------------------------- commit 62165600ae73ebd76e2d9b992b36360408d570d8 Author: Steven Rostedt (VMware) rostedt@goodmis.org Date: Fri Oct 5 10:08:03 2018 -0400
vsprintf: Fix off-by-one bug in bstr_printf() processing dereferenced pointers
The functions vbin_printf() and bstr_printf() are used by trace_printk() to try to keep the overhead down during printing. trace_printk() uses vbin_printf() at the time of execution, as it only scans the fmt string to record the printf values into the buffer, and then uses vbin_printf() to do the conversions to print the string based on the format and the saved values in the buffer.
This is an issue for dereferenced pointers, as before commit 841a915d20c7b, the processing of the pointer could happen some time after the pointer value was recorded (reading the trace buffer). This means the processing of the value at a later time could show different results, or even crash the system, if the pointer no longer existed.
Commit 841a915d20c7b addressed this by processing dereferenced pointers at the time of execution and save the result in the ring buffer as a string. The bstr_printf() would then treat these pointers as normal strings, and print the value. But there was an off-by-one bug here, where after processing the argument, it move the pointer only "strlen(arg)" which made the arg pointer not point to the next argument in the ring buffer, but instead point to the nul character of the last argument. This causes any values after a dereferenced pointer to be corrupted.
Cc: stable@vger.kernel.org Fixes: 841a915d20c7b ("vsprintf: Do not have bprintf dereference pointers") Reported-by: Nikolay Borisov nborisov@suse.com Tested-by: Nikolay Borisov nborisov@suse.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index d5b3a3f95c01..812e59e13fe6 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -2794,7 +2794,7 @@ int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf) copy = end - str; memcpy(str, args, copy); str += len; - args += len; + args += len + 1; } } if (process)