From c540b2cdd42850d80502f7ca7209385e16a4e8d6 Mon Sep 17 00:00:00 2001 From: Mauricio Faria de Oliveira Date: Wed, 14 Feb 2024 18:47:19 +0100 Subject: [PATCH] fix undefined path_max for st_size zero Bug-Ubuntu: https://bugs.launchpad.net/bugs/1792647 Bug-Debian: https://bugs.debian.org/909011 Reviewed-by: dod The downstream 'path_max' patch in Debian sets the buffer size for readlink() to the 'st_size' value obtained with lstat(). However, it might be zero for some symlinks in /proc on Linux (notably /proc/self) leading to readlink() failing with EINVAL. $ strace -e lstat stat /proc/self 2>&1 \ | grep -e lstat -e File: -e Size: lstat("/proc/self", {st_mode=S_IFLNK|0777, st_size=0, ...}) = 0 File: /proc/self -> 30875 Size: 0 Blocks: 0 IO Block: 1024 symbolic link This causes readlink (tool) to files like /dev/stdin to fail, which may link to /proc/self/fd/0 on containers or elsewhere. Test-case: ubuntu@cosmic:~/node$ $ strace -E LD_LIBRARY_PATH=/usr/local/lib/ -f -e lstat,readlink \ node test/parallel/test-fs-realpath-pipe.js With path_max: [pid 17785] lstat("/dev", {st_mode=S_IFDIR|0755, st_size=480, ...}) = 0 [pid 17786] lstat("/dev/stdin", {st_mode=S_IFLNK|0777, st_size=15, ...}) = 0 [pid 17788] lstat("/dev/stdin", {st_mode=S_IFLNK|0777, st_size=15, ...}) = 0 [pid 17788] readlink("/dev/stdin", "/proc/self/fd/0", 15) = 15 [pid 17785] lstat("/proc", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0 [pid 17786] lstat("/proc/self", {st_mode=S_IFLNK|0777, st_size=0, ...}) = 0 [pid 17788] lstat("/proc/self", {st_mode=S_IFLNK|0777, st_size=0, ...}) = 0 [pid 17788] readlink("/proc/self", 0x7f2a6c000b40, 0) = -1 EINVAL (Invalid argument) Without path_max: [pid 18114] lstat("/dev", {st_mode=S_IFDIR|0755, st_size=480, ...}) = 0 [pid 18114] lstat("/dev/stdin", {st_mode=S_IFLNK|0777, st_size=15, ...}) = 0 [pid 18114] readlink("/dev/stdin", "/proc/self/fd/0", 4096) = 15 [pid 18114] lstat("/proc", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0 [pid 18114] lstat("/proc/self", {st_mode=S_IFLNK|0777, st_size=0, ...}) = 0 [pid 18114] readlink("/proc/self", "18114", 4096) = 5 [pid 18114] lstat("/proc/18114", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0 [pid 18114] lstat("/proc/18114/fd", {st_mode=S_IFDIR|0500, st_size=0, ...}) = 0 [pid 18114] lstat("/proc/18114/fd/0", {st_mode=S_IFLNK|0700, st_size=64, ...}) = 0 [pid 18114] readlink("/proc/18114/fd/0", "socket:[199607]", 4096) = 15 With this patch on top of path_max: [pid 18433] lstat("/dev", {st_mode=S_IFDIR|0755, st_size=480, ...}) = 0 [pid 18433] lstat("/dev/stdin", {st_mode=S_IFLNK|0777, st_size=15, ...}) = 0 [pid 18433] lstat("/dev/stdin", {st_mode=S_IFLNK|0777, st_size=15, ...}) = 0 [pid 18433] readlink("/dev/stdin", "/proc/self/fd/0", 15) = 15 [pid 18433] lstat("/proc", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0 [pid 18433] lstat("/proc/self", {st_mode=S_IFLNK|0777, st_size=0, ...}) = 0 [pid 18433] lstat("/proc/self", {st_mode=S_IFLNK|0777, st_size=0, ...}) = 0 [pid 18433] readlink("/proc/self", "18433", 256) = 5 [pid 18433] lstat("/proc/18433", {st_mode=S_IFDIR|0555, st_size=0, ...}) = 0 [pid 18433] lstat("/proc/18433/fd", {st_mode=S_IFDIR|0500, st_size=0, ...}) = 0 [pid 18433] lstat("/proc/18433/fd/0", {st_mode=S_IFLNK|0700, st_size=64, ...}) = 0 [pid 18433] lstat("/proc/18433/fd/0", {st_mode=S_IFLNK|0700, st_size=64, ...}) = 0 [pid 18433] readlink("/proc/18433/fd/0", "socket:[191351]", 64) = 15 Reviewed-by: dod Gbp-Pq: Name path_max_zero_st_size --- src/unix/fs.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/src/unix/fs.c b/src/unix/fs.c index 3a74350..4968293 100644 --- a/src/unix/fs.c +++ b/src/unix/fs.c @@ -657,6 +657,17 @@ static ssize_t uv__fs_readlink(uv_fs_t* req) { maxlen = uv__fs_pathmax_size(req->path); #endif + /* Some symlinks in /proc report st_size == 0 */ + if (maxlen == 0) { +#if defined(_POSIX_PATH_MAX) + maxlen = _POSIX_PATH_MAX; +#elif defined(PATH_MAX) + maxlen = PATH_MAX; +#else + maxlen = 4096; /* fallback */ +#endif + } + buf = uv__malloc(maxlen); if (buf == NULL) { -- 2.30.2