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Subject[PATCH] seq_file: seq_show_option_n() is used for precise sizes
Date
When seq_show_option_n() is used, it is for non-string memory that
happens to be printable bytes. As such, we must use memcpy() to copy the
bytes and then explicitly NUL-terminate the result.

Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/linux/seq_file.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index bd023dd38ae6..386ab580b839 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -249,18 +249,19 @@ static inline void seq_show_option(struct seq_file *m, const char *name,

/**
* seq_show_option_n - display mount options with appropriate escapes
- * where @value must be a specific length.
+ * where @value must be a specific length (i.e.
+ * not NUL-terminated).
* @m: the seq_file handle
* @name: the mount option name
* @value: the mount option name's value, cannot be NULL
- * @length: the length of @value to display
+ * @length: the exact length of @value to display, must be constant expression
*
* This is a macro since this uses "length" to define the size of the
* stack buffer.
*/
#define seq_show_option_n(m, name, value, length) { \
char val_buf[length + 1]; \
- strncpy(val_buf, value, length); \
+ memcpy(val_buf, value, length); \
val_buf[length] = '\0'; \
seq_show_option(m, name, val_buf); \
}
--
2.34.1
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