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From: "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>
To: rostedt@goodmis.org
Cc: linux-trace-devel@vger.kernel.org
Subject: [PATCH 1/3] trace-cmd: Fix segmentation fault in tracecmd_read_at() in specific use case
Date: Fri, 11 Oct 2019 14:30:47 +0300
Message-ID: <20191011113047.11089-1-tz.stoyanov@gmail.com> (raw)

There is a segmentation fault in update_page_info() when the requested page
is not loaded, handle->cpu_data[cpu].page is NULL. The problematic flow starts
from tracecmd_read_at() API, when reading offset in the first page (less than 4K),
and this page is still not loaded. The problem can be observed randomly - there is
a sporadic KernelShark crash when loading a file, browsing and zooming events.

https://bugzilla.kernel.org/show_bug.cgi?id=205165
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 lib/trace-cmd/trace-input.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
index 60ee2f7..1ae2ab5 100644
--- a/lib/trace-cmd/trace-input.c
+++ b/lib/trace-cmd/trace-input.c
@@ -1345,7 +1345,8 @@ tracecmd_read_at(struct tracecmd_input *handle, unsigned long long offset,
 	/* check to see if we have this page already */
 	for (cpu = 0; cpu < handle->cpus; cpu++) {
 		if (handle->cpu_data[cpu].offset == page_offset &&
-		    handle->cpu_data[cpu].file_size)
+		    handle->cpu_data[cpu].file_size &&
+		    handle->cpu_data[cpu].page)
 			break;
 	}
 
-- 
2.21.0


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