* Rich Felker: > There's a longstanding unfixable (due to API stability) bug in the > pwrite syscall: > > http://man7.org/linux/man-pages/man2/pwrite.2.html#BUGS > > whereby it wrongly honors O_APPEND if set, ignoring the caller-passed > offset. Now that there's a pwritev2 syscall that takes a flags > argument, it's possible to fix this without breaking stability by > adding a new RWF_NOAPPEND flag, which callers that want the fixed > behavior can then pass. > > I have a completely untested patch to add such a flag, but would like > to get a feel for whether the concept is acceptable before putting > time into testing it. If so, I'll submit this as a proper patch with > detailed commit message etc. Draft is below. Has this come up before? I had already written a test case and it turns out that an O_APPEND descriptor does not protect the previously written data in the file: openat(AT_FDCWD, "/tmp/append-truncateuoRexJ", O_RDWR|O_CREAT|O_EXCL, 0600) = 3 write(3, "@", 1) = 1 close(3) = 0 openat(AT_FDCWD, "/tmp/append-truncateuoRexJ", O_WRONLY|O_APPEND) = 3 ftruncate(3, 0) = 0 So at least it looks like there is no security issue in adding a RWF_NOAPPEND flag. Thanks, Florian
