From: Marcin Slusarz Date: Tue, 27 Jul 2010 23:18:01 +0000 (+0200) Subject: tracing: Sanitize value returned from write(trace_marker, "...", len) X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=1aa54bca6ee0d07ebcafb8ca8074b624d80724aa;p=linux-beck.git tracing: Sanitize value returned from write(trace_marker, "...", len) When userspace code writes non-new-line-terminated string to trace_marker file, write handler appends new-line and returns number of bytes written to trace buffer, so write(fd, "abc", 3) will return 4 That's unexpected and unfortunately it confuses glibc's fprintf function. Example: int main() { fprintf(stderr, "abc"); return 0; } $ gcc test.c -o test $ echo mmiotrace > /sys/kernel/debug/tracing/current_tracer $ ./test 2>/sys/kernel/debug/tracing/trace_marker results in infinite loop: write(fd, "abc", 3) = 4 write(fd, "", 1) = 0 write(fd, "", 1) = 0 write(fd, "", 1) = 0 write(fd, "", 1) = 0 write(fd, "", 1) = 0 write(fd, "", 1) = 0 write(fd, "", 1) = 0 (...) ...and kernel trace buffer full of empty markers. Fix it by sanitizing write return value. Signed-off-by: Marcin Slusarz LKML-Reference: <20100727231801.GB2826@joi.lan> Cc: Frederic Weisbecker Cc: Ingo Molnar Signed-off-by: Steven Rostedt --- diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 086d36316805..88b42d14d32d 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3498,6 +3498,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf, size_t cnt, loff_t *fpos) { char *buf; + size_t written; if (tracing_disabled) return -EINVAL; @@ -3519,11 +3520,15 @@ tracing_mark_write(struct file *filp, const char __user *ubuf, } else buf[cnt] = '\0'; - cnt = mark_printk("%s", buf); + written = mark_printk("%s", buf); kfree(buf); - *fpos += cnt; + *fpos += written; - return cnt; + /* don't tell userspace we wrote more - it might confuse them */ + if (written > cnt) + written = cnt; + + return written; } static int tracing_clock_show(struct seq_file *m, void *v)