From 9b646f5dc933dfa019f2ed7f80b6198b43e31f62 Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Date: Tue, 18 Feb 2025 15:58:16 -0500 Subject: elf: Canonicalize $ORIGIN in an explicit ld.so invocation [BZ 25263] When an executable is invoked directly, we calculate $ORIGIN by calling readlink on /proc/self/exe, which the Linux kernel resolves to the target of any symlinks. However, if an executable is run through ld.so, we cannot use /proc/self/exe and instead use the path given as an argument. This leads to a different calculation of $ORIGIN, which is most notable in that it causes ldd to behave differently (e.g., by not finding a library) from directly running the program. To make the behavior consistent, take advantage of the fact that the kernel also resolves /proc/self/fd/ symlinks to the target of any symlinks in the same manner, so once we have opened the main executable in order to load it, replace the user-provided path with the result of calling readlink("/proc/self/fd/N"). (On non-Linux platforms this resolution does not happen and so no behavior change is needed.) The __fd_to_filename requires _fitoa_word and _itoa_word, which for 32-bits pulls a lot of definitions from _itoa.c (due _ITOA_NEEDED being defined). To simplify the build move the required function to a new file, _fitoa_word.c. Checked on x86_64-linux-gnu and i686-linux-gnu. Co-authored-by: Geoffrey Thomas Reviewed-by: Geoffrey Thomas Tested-by: Geoffrey Thomas --- sysdeps/unix/sysv/linux/dl-origin.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) (limited to 'sysdeps/unix/sysv/linux') diff --git a/sysdeps/unix/sysv/linux/dl-origin.c b/sysdeps/unix/sysv/linux/dl-origin.c index decdd8a..3c52ba5 100644 --- a/sysdeps/unix/sysv/linux/dl-origin.c +++ b/sysdeps/unix/sysv/linux/dl-origin.c @@ -21,6 +21,7 @@ #include #include #include +#include /* On Linux >= 2.1 systems which have the dcache implementation we can get the path of the application from the /proc/self/exe symlink. Try this @@ -72,3 +73,25 @@ _dl_get_origin (void) return result; } + +/* On Linux, readlink on the magic symlinks in /proc/self/fd also has + the same behavior of returning the canonical path from the dcache. + If it does not work, we do not bother to canonicalize. */ + +char * +_dl_canonicalize (int fd) +{ + struct fd_to_filename fdfilename; + char canonical[PATH_MAX]; + char *path = __fd_to_filename (fd, &fdfilename); + int size = INTERNAL_SYSCALL_CALL (readlinkat, AT_FDCWD, path, + canonical, PATH_MAX - 1); + + /* Check if the path was truncated. */ + if (size >= 0 && size < PATH_MAX - 1) + { + canonical[size] = '\0'; + return __strdup (canonical); + } + return NULL; +} -- cgit v1.1