“5) A failure of the stat() system call is not an accurate indicator of the exec()-ability of the file. The only way to determine if a file is executable is to execute it.”
This is not generally true. We need to check for +x, and there was something with strange operating systems, *and* the shell does not only use the exec*() family syscalls but also “executes” a script by doing stuff itself. I’m willing to compromise on the error message right now. Everything else needs more thought, and (probably) tomorrow will see a new mksh version. -- You received this bug notification because you are a member of mksh Mailing List, which is subscribed to mksh. Matching subscriptions: mkshlist-to-mksh-bugmail https://bugs.launchpad.net/bugs/1817789 Title: misleading error message for SELinux denials Status in mksh: Opinion Bug description: Given a stat(2) failure caused by an SELinux denial (rather than a stat(2) success and an access(2) failure, as with a regular `chmod a-x` failure), mksh reports "not found" rather than the more correct "Permission denied". Expected: * Permission Denied error message Actual: $ sh -c /system/bin/vold sh: /system/bin/vold: not found "not found" error message. here's the behind-the-scenes SELinux denial: 02-25 22:37:11.023 4571 4571 W sh : type=1400 audit(0.0:347): avc: denied { getattr } for path="/system/bin/vold" dev="dm-0" ino=717 scontext=u:r:shell:s0 tcontext=u:object_r:vold_exec:s0 tclass=file permissive=0 here's what strace says happened: newfstatat(AT_FDCWD, "/system/bin/vold", 0x7ffcc3ef20, 0) = -1 EACCES (Permission denied) write(2, "/system/bin/sh: /system/bin/vold"..., 44/system/bin/sh: /system/bin/vold: not found ) = 44 versus the normal `chmod a-x` case where stat succeeds but access fails: newfstatat(AT_FDCWD, "/data/local/tmp/date2", {st_mode=S_IFREG|0644, st_size=482560, ...}, 0) = 0 faccessat(AT_FDCWD, "/data/local/tmp/date2", X_OK) = -1 EACCES (Permission denied) write(2, "sh: /data/local/tmp/date2: can't"..., 60sh: /data/local/tmp/date2: can't execute: Permission denied ) = 60 this patch fixes the issue: ``` diff --git a/src/exec.c b/src/exec.c index 8330174..3f6d876 100644 --- a/src/exec.c +++ b/src/exec.c @@ -1279,8 +1279,8 @@ search_access(const char *fn, int mode) struct stat sb; if (stat(fn, &sb) < 0) - /* file does not exist */ - return (ENOENT); + /* file may or may not exist: check errno */ + return errno; /* LINTED use of access */ if (access(fn, mode) < 0) { /* file exists, but we can't access it */ ``` i don't know if you want to elaborate further in the comment along the lines of "...for example, an SELinux denial may mean that we get EACCES here, or if the file doesn't exist and we're allowed to know that, we'll get ENOENT". result with patch: $ sh -c /system/bin/vold sh: /system/bin/vold: can't execute: Permission denied To manage notifications about this bug go to: https://bugs.launchpad.net/mksh/+bug/1817789/+subscriptions
