This patch just trades one undefined behaviour for another. I'd open first and then do fstat. Otherwise change your comment, because it isn't really enforcing anything with a race condition between the stat and the open.
Sam On Tue, Jan 5, 2016 at 11:50 AM, Ari Sundholm <[email protected]> wrote: > We need to enforce that the opened file is a block device, as > opening a file with the O_EXCL flag on and the O_CREATE flag off has > undefined behavior unless the file is a block device. > > Signed-off-by: Ari Sundholm <[email protected]> > --- > util-linux/blkdiscard.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/util-linux/blkdiscard.c b/util-linux/blkdiscard.c > index ace88a1..1b234fa 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 +51,15 @@ int blkdiscard_main(int argc UNUSED_PARAM, char **argv) > opts = getopt32(argv, "o:l:s", &offset_str, &length_str); > argv += optind; > > + /* We need to enforce that the opened file is a block device, as > + * opening a file with the O_EXCL flag on and the O_CREATE flag > off has > + * undefined behavior unless the file is a block device. > + */ > + 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 > > > > _______________________________________________ > busybox mailing list > [email protected] > http://lists.busybox.net/mailman/listinfo/busybox >
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