[PATCH] drivers/base: Fix length checks increate_syslog_header()/dev_vprintk_emit()

From: Ben Hutchings
Date: Fri Dec 27 2013 - 12:18:37 EST

snprintf() returns the number of bytes that could have been written
(excluding the null), not the actual number of bytes written. Given a
long enough subsystem or device name, these functions will advance
beyond the end of the on-stack buffer in dev_vprintk_exit(), resulting
in an information leak or stack corruption. I don't know whether such
a long name is currently possible.

In case snprintf() returns a value >= the buffer size, do not add
structured logging information. Also WARN the first time this
happens, so we can fix the driver or increase the buffer size.

Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
drivers/base/core.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 67b180d..989a93c 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2022,6 +2022,8 @@ create_syslog_header(const struct device *dev, char *hdr, size_t hdrlen)
return 0;

pos += snprintf(hdr + pos, hdrlen - pos, "SUBSYSTEM=%s", subsys);
+ if (pos >= hdrlen)
+ goto overflow;

* Add device identifier DEVICE=:
@@ -2053,7 +2055,14 @@ create_syslog_header(const struct device *dev, char *hdr, size_t hdrlen)
"DEVICE=+%s:%s", subsys, dev_name(dev));

+ if (pos >= hdrlen)
+ goto overflow;
return pos;
+ dev_WARN_ONCE(dev, 1, "device/subsystem name too long");
+ return 0;

Ben Hutchings
Computers are not intelligent. They only think they are.

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