From: Justin Stitt justinstitt@google.com
mainline inclusion from mainline-v6.7-rc1 commit ceb0416383988dbd5decd6a70141a3507732c160 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8T02O
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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`strncpy` is deprecated for use on NUL-terminated destination strings [1] and as such we should prefer more robust and less ambiguous string interfaces.
There are three such strncpy uses that this patch addresses:
The respective destination buffers are: 1) mddev->clevel 2) clevel 3) mddev->metadata_type
We expect mddev->clevel to be NUL-terminated due to its use with format strings: | ret = sprintf(page, "%s\n", mddev->clevel);
Furthermore, we can see that mddev->clevel is not expected to be NUL-padded as `md_clean()` merely set's its first byte to NULL -- not the entire buffer: | static void md_clean(struct mddev *mddev) | { | mddev->array_sectors = 0; | mddev->external_size = 0; | ... | mddev->level = LEVEL_NONE; | mddev->clevel[0] = 0; | ...
A suitable replacement for this instance is `memcpy` as we know the number of bytes to copy and perform manual NUL-termination at a specified offset. This really decays to just a byte copy from one buffer to another. `strscpy` is also a considerable replacement but using `slen` as the length argument would result in truncation of the last byte unless something like `slen + 1` was provided which isn't the most idiomatic strscpy usage.
For the next case, the destination buffer `clevel` is expected to be NUL-terminated based on its usage within kstrtol() which expects NUL-terminated strings. Note that, in context, this code removes a trailing newline which is seemingly not required as kstrtol() can handle trailing newlines implicitly. However, there exists further usage of clevel (or buf) that would also like to have the newline removed. All in all, with similar reasoning to the first case, let's just use memcpy as this is just a byte copy and NUL-termination is handled manually.
The third and final case concerning `mddev->metadata_type` is more or less the same as the other two. We expect that it be NUL-terminated based on its usage with seq_printf: | seq_printf(seq, " super external:%s", | mddev->metadata_type); ... and we can surmise that NUL-padding isn't required either due to how it is handled in md_clean(): | static void md_clean(struct mddev *mddev) | { | ... | mddev->metadata_type[0] = 0; | ...
So really, all these instances have precisely calculated lengths and purposeful NUL-termination so we can just use memcpy to remove ambiguity surrounding strncpy.
Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nu... [1] Link: https://github.com/KSPP/linux/issues/90 Cc: linux-hardening@vger.kernel.org Signed-off-by: Justin Stitt justinstitt@google.com Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: Song Liu song@kernel.org Link: https://lore.kernel.org/r/20230925-strncpy-drivers-md-md-c-v1-1-2b0093b89c2b... Signed-off-by: Li Nan linan122@huawei.com --- drivers/md/md.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c index 7c46d83af3cd..fe164002c1ef 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -3914,7 +3914,7 @@ level_store(struct mddev *mddev, const char *buf, size_t len) return rv;
if (mddev->pers == NULL) { - strncpy(mddev->clevel, buf, slen); + memcpy(mddev->clevel, buf, slen); if (mddev->clevel[slen-1] == '\n') slen--; mddev->clevel[slen] = 0; @@ -3947,7 +3947,7 @@ level_store(struct mddev *mddev, const char *buf, size_t len) }
/* Now find the new personality */ - strncpy(clevel, buf, slen); + memcpy(clevel, buf, slen); if (clevel[slen-1] == '\n') slen--; clevel[slen] = 0; @@ -4733,7 +4733,7 @@ metadata_store(struct mddev *mddev, const char *buf, size_t len) size_t namelen = len-9; if (namelen >= sizeof(mddev->metadata_type)) namelen = sizeof(mddev->metadata_type)-1; - strncpy(mddev->metadata_type, buf+9, namelen); + memcpy(mddev->metadata_type, buf+9, namelen); mddev->metadata_type[namelen] = 0; if (namelen && mddev->metadata_type[namelen-1] == '\n') mddev->metadata_type[--namelen] = 0;