[PATCH v3] drivers/base: Fix length checks in create_syslog_header()/dev_vprintk_emit()

From: Ben Hutchings
Date: Tue Aug 26 2014 - 03:35:04 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 if this happens, so we can
fix the driver or increase the buffer size.

Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
v2: use dev_WARN() not dev_WARN_ON()
v3: the version that actually compiles

drivers/base/core.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 20da3ad..28b808c 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2007,6 +2007,8 @@ 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=:
@@ -2038,7 +2040,14 @@ 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(dev, "device/subsystem name too long");
+ return 0;

int dev_vprintk_emit(int level, const struct device *dev,

Ben Hutchings
No political challenge can be met by shopping. - George Monbiot

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