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libuv: do not require PATH_MAX to be defined

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Some platforms (e.g. GNU/Hurd) do not define PATH_MAX.  Add a few other
variants and a fallback constant.  Also use alternatives where possible:

* For readlink(), use lstat() to read the length of the link first.
  If it is not a symlink, report EINVAL before trying to allocate.
  If the size reports as zero, fall back one of the PATH_MAX variants.

* For realpath(), POSIX 2008 allows us to pass a NULL buffer
  to tell it to malloc() internally.

This patch was inspired by downstream patches in Debian packaging
for issues 897061 and 909011.

Issue: #18337
This commit is contained in:
Brad King
2018-09-28 12:41:12 -04:00
parent f478fa633d
commit 3c0bfb596f
1 changed files with 39 additions and 8 deletions
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47
Utilities/cmlibuv/src/unix/fs.c
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@@ -425,19 +425,22 @@ static ssize_t uv__fs_scandir(uv_fs_t* req) {
return n; return n;
} }
#if defined(_POSIX_PATH_MAX)
# define UV__FS_PATH_MAX _POSIX_PATH_MAX
#elif defined(PATH_MAX)
# define UV__FS_PATH_MAX PATH_MAX
#else
# define UV__FS_PATH_MAX_FALLBACK 8192
# define UV__FS_PATH_MAX UV__FS_PATH_MAX_FALLBACK
#endif
static ssize_t uv__fs_pathmax_size(const char* path) { static ssize_t uv__fs_pathmax_size(const char* path) {
ssize_t pathmax; ssize_t pathmax;
pathmax = pathconf(path, _PC_PATH_MAX); pathmax = pathconf(path, _PC_PATH_MAX);
if (pathmax == -1) { if (pathmax == -1)
#if defined(PATH_MAX) pathmax = UV__FS_PATH_MAX;
return PATH_MAX;
#else
#error "PATH_MAX undefined in the current platform"
#endif
}
return pathmax; return pathmax;
} }
@@ -446,7 +449,28 @@ static ssize_t uv__fs_readlink(uv_fs_t* req) {
ssize_t len; ssize_t len;
char* buf; char* buf;
#if defined(UV__FS_PATH_MAX_FALLBACK)
/* We may not have a real PATH_MAX. Read size of link. */
struct stat st;
int ret;
ret = lstat(req->path, &st);
if (ret != 0)
return -1;
if (!S_ISLNK(st.st_mode)) {
errno = EINVAL;
return -1;
}
len = st.st_size;
/* According to readlink(2) lstat can report st_size == 0
for some symlinks, such as those in /proc or /sys. */
if (len == 0)
len = uv__fs_pathmax_size(req->path); len = uv__fs_pathmax_size(req->path);
#else
len = uv__fs_pathmax_size(req->path);
#endif
buf = uv__malloc(len + 1); buf = uv__malloc(len + 1);
if (buf == NULL) { if (buf == NULL) {
@@ -473,9 +497,15 @@ static ssize_t uv__fs_readlink(uv_fs_t* req) {
} }
static ssize_t uv__fs_realpath(uv_fs_t* req) { static ssize_t uv__fs_realpath(uv_fs_t* req) {
ssize_t len;
char* buf; char* buf;
#if defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L
buf = realpath(req->path, NULL);
if (buf == NULL)
return -1;
#else
ssize_t len;
len = uv__fs_pathmax_size(req->path); len = uv__fs_pathmax_size(req->path);
buf = uv__malloc(len + 1); buf = uv__malloc(len + 1);
@@ -488,6 +518,7 @@ static ssize_t uv__fs_realpath(uv_fs_t* req) {
uv__free(buf); uv__free(buf);
return -1; return -1;
} }
#endif
req->ptr = buf; req->ptr = buf;