From e2fa720be7024cce4fc489f3877476d35da48ee2 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Mon, 23 Nov 2020 19:44:19 -0500 Subject: [PATCH] work around linux bug in readlink syscall with zero buffer size linux fails with EINVAL when a zero buffer size is passed to the syscall. this is non-conforming because POSIX already defines EINVAL with a significantly different meaning: the target is not a symlink. since the request is semantically valid, patch it up by using a dummy buffer of length one, and truncating the return value to zero if it succeeds. --- src/unistd/readlink.c | 11 +++++++++-- src/unistd/readlinkat.c | 9 ++++++++- 2 files changed, 17 insertions(+), 3 deletions(-) diff --git a/src/unistd/readlink.c b/src/unistd/readlink.c index a152d524..32f4537f 100644 --- a/src/unistd/readlink.c +++ b/src/unistd/readlink.c @@ -4,9 +4,16 @@ ssize_t readlink(const char *restrict path, char *restrict buf, size_t bufsize) { + char dummy[1]; + if (!bufsize) { + buf = dummy; + bufsize = 1; + } #ifdef SYS_readlink - return syscall(SYS_readlink, path, buf, bufsize); + int r = __syscall(SYS_readlink, path, buf, bufsize); #else - return syscall(SYS_readlinkat, AT_FDCWD, path, buf, bufsize); + int r = __syscall(SYS_readlinkat, AT_FDCWD, path, buf, bufsize); #endif + if (buf == dummy && r > 0) r = 0; + return __syscall_ret(r); } diff --git a/src/unistd/readlinkat.c b/src/unistd/readlinkat.c index 9af45cd5..f79d3d14 100644 --- a/src/unistd/readlinkat.c +++ b/src/unistd/readlinkat.c @@ -3,5 +3,12 @@ ssize_t readlinkat(int fd, const char *restrict path, char *restrict buf, size_t bufsize) { - return syscall(SYS_readlinkat, fd, path, buf, bufsize); + char dummy[1]; + if (!bufsize) { + buf = dummy; + bufsize = 1; + } + int r = __syscall(SYS_readlinkat, fd, path, buf, bufsize); + if (buf == dummy && r > 0) r = 0; + return __syscall_ret(r); }