Opening a file with the O_EXCL flag on and the O_CREAT flag off has
undefined behavior unless the file is a block device. Let's try and
avoid this case on a best-effort basis. The undefined behavior can
still be hit if the block device is replaced with something else
inbetween.
v2: Fix typo: O_CREAT, not O_CREATE.
v3: Change the comment, as the condition is not actually enforced,
only checked on a best-effort basis.
Signed-off-by: Ari Sundholm <[email protected]>
---
util-linux/blkdiscard.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/util-linux/blkdiscard.c b/util-linux/blkdiscard.c
index ace88a1..b97f716 100644
--- a/util-linux/blkdiscard.c
+++ b/util-linux/blkdiscard.c
@@ -38,7 +38,7 @@ int blkdiscard_main(int argc UNUSED_PARAM, char **argv)
uint64_t offset; /* Leaving these two variables out does not */
uint64_t length; /* shrink code size and hampers readability. */
uint64_t range[2];
-// struct stat st;
+ struct stat st;
int fd;
enum {
@@ -51,11 +51,17 @@ int blkdiscard_main(int argc UNUSED_PARAM, char **argv)
opts = getopt32(argv, "o:l:s", &offset_str, &length_str);
argv += optind;
+ /* Opening a file with the O_EXCL flag on and the O_CREAT flag off has
+ * undefined behavior unless the file is a block device. Let's try and
+ * avoid this case on a best-effort basis. The undefined behavior can
+ * still be hit if the block device is replaced with something else
+ * inbetween.
+ */
+ xstat(argv[0], &st);
+ if (!S_ISBLK(st.st_mode))
+ bb_error_msg_and_die("%s: not a block device", argv[0]);
+
fd = xopen(argv[0], O_RDWR|O_EXCL);
-//Why bother, BLK[SEC]DISCARD will fail on non-blockdevs anyway?
-// xfstat(fd, &st);
-// if (!S_ISBLK(st.st_mode))
-// bb_error_msg_and_die("%s: not a block device", argv[0]);
offset = xatoull_sfx(offset_str, kMG_suffixes);
--
1.9.1
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