unlink_file: strip trailing slashes

If the user replaces a directory with a symlink, libalpm would get
confused because the trailing slash causes system calls to resolve the
symlink.  This leads to errors and a misleading message during upgrades.
Even though libalpm does not support this, it should not be giving
misleading errors.

Also adds an overflow check.

Fixes FS#51377

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
(cherry picked from commit 16b91f798faf6413f9b043543c5c0c3467b6fdbf)

3 files changed, 29 insertions, 1 deletions

diff --git a/lib/libalpm/remove.c b/lib/libalpm/remove.c
index 173dbc69..ee8f288e 100644
--- a/lib/libalpm/remove.c
+++ b/lib/libalpm/remove.c
@@ -440,8 +440,19 @@ static int unlink_file(alpm_handle_t *handle, alpm_pkg_t *oldpkg,
 {
 	struct stat buf;
 	char file[PATH_MAX];
+	int file_len;
 
-	snprintf(file, PATH_MAX, "%s%s", handle->root, fileobj->name);
+	file_len = snprintf(file, PATH_MAX, "%s%s", handle->root, fileobj->name);
+	if(file_len <= 0 || file_len >= PATH_MAX) {
+		/* 0 is a valid value from snprintf, but should be impossible here */
+		_alpm_log(handle, ALPM_LOG_DEBUG, "path too long to unlink %s%s\n",
+				handle->root, fileobj->name);
+		return -1;
+	} else if(file[file_len-1] == '/') {
+		/* trailing slashes cause errors and confusing messages if the user has
+		 * replaced a directory with a symlink */
+		file[--file_len] = '\0';
+	}
 
 	if(llstat(file, &buf)) {
 		_alpm_log(handle, ALPM_LOG_DEBUG, "file %s does not exist\n", file);
diff --git a/test/pacman/tests/TESTS b/test/pacman/tests/TESTS
index 81078a58..9da24589 100644
--- a/test/pacman/tests/TESTS
+++ b/test/pacman/tests/TESTS
@@ -109,6 +109,7 @@ TESTS += test/pacman/tests/querycheck002.py
 TESTS += test/pacman/tests/querycheck_fast_file_type.py
 TESTS += test/pacman/tests/reason001.py
 TESTS += test/pacman/tests/remove-assumeinstalled.py
+TESTS += test/pacman/tests/remove-directory-replaced-with-symlink.py
 TESTS += test/pacman/tests/remove-optdepend-of-installed-package.py
 TESTS += test/pacman/tests/remove-recursive-cycle.py
 TESTS += test/pacman/tests/remove001.py
diff --git a/test/pacman/tests/remove-directory-replaced-with-symlink.py b/test/pacman/tests/remove-directory-replaced-with-symlink.py
new file mode 100644
index 00000000..37be7579
--- /dev/null
+++ b/test/pacman/tests/remove-directory-replaced-with-symlink.py
@@ -0,0 +1,16 @@
+self.description = "remove a package with a directory that has been replaced with a symlink"
+
+self.filesystem = [ "var/", "srv -> var/" ]
+
+lpkg = pmpkg("pkg1")
+lpkg.files = ["srv/"]
+self.addpkg2db("local", lpkg)
+
+self.args = "-R %s" % (lpkg.name)
+
+self.addrule("PACMAN_RETCODE=0")
+self.addrule("DIR_EXIST=var/")
+self.addrule("!LINK_EXIST=srv")
+self.addrule("!FILE_EXIST=srv")
+self.addrule("!DIR_EXIST=srv")
+self.addrule("!PACMAN_OUTPUT=cannot remove")