Convert some sprintf() calls to kmem_scnprintf()

These `sprintf()` calls are used repeatedly to write to a buffer. There
is no protection against overflow other than reviewers explicitly
checking to see if the buffers are big enough. However, such issues are
easily missed during review and when they are missed, we would rather
stop printing rather than have a buffer overflow, so we convert these
functions to use `kmem_scnprintf()`. The Linux kernel provides an entire
page for module parameters, so we are safe to write up to PAGE_SIZE.

Removing `sprintf()` from these functions removes the last instances of
`sprintf()` usage in our platform-independent kernel code. This improves
XNU kernel compatibility because the XNU kernel does not support
(removed support for?) `sprintf()`.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Jorgen Lundman <[email protected]>
Signed-off-by: Richard Yao <[email protected]>
Closes #14209 

1 files changed, 2 insertions, 2 deletions

diff --git a/module/zcommon/zfs_fletcher.c b/module/zcommon/zfs_fletcher.c
index 9a201842e..44c8f486f 100644
--- a/module/zcommon/zfs_fletcher.c
+++ b/module/zcommon/zfs_fletcher.c
@@ -903,12 +903,12 @@ fletcher_4_param_get(char *buffer, zfs_kernel_param_t *unused)
 
 	/* list fastest */
 	fmt = IMPL_FMT(impl, IMPL_FASTEST);
-	cnt += sprintf(buffer + cnt, fmt, "fastest");
+	cnt += kmem_scnprintf(buffer + cnt, PAGE_SIZE - cnt, fmt, "fastest");
 
 	/* list all supported implementations */
 	for (uint32_t i = 0; i < fletcher_4_supp_impls_cnt; ++i) {
 		fmt = IMPL_FMT(impl, i);
-		cnt += sprintf(buffer + cnt, fmt,
+		cnt += kmem_scnprintf(buffer + cnt, PAGE_SIZE - cnt, fmt,
 		    fletcher_4_supp_impls[i]->name);
 	}