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ash: command -v CMD must skip (go to next path) when CMD exists, but is not executable

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Upstream commit:

    Date: Fri, 5 Apr 2024 17:55:46 +0800
    exec: Check executable bit when searching path

    Andrej Shadura <andrew.shadura@collabora.co.uk> wrote:
    ...
    > https://bugs.debian.org/874264
    > -------- Forwarded Message --------
    > Subject: dash: 'command -v' mistakenly returns a shell script whose
    > executable is not set
    > Date: Mon, 04 Sep 2017 10:45:48 -0400
    > From: Norman Ramsey <nr@cs.tufts.edu>
    > To: Debian Bug Tracking System <submit@bugs.debian.org>
    ...
    > I tracked a build bug in s-nail to a problem with dash.  Symptom:
    > building s-nail tries to run /home/nr/bin/clang, a script whose
    > executable bit is not set.  We tracked the problem to the result of
    > running `command -v clang` with /bin/sh:
    ...
    This is inherited from NetBSD.  There is even a commented-out
    block of code that tried to fix this.

    Anyway, we now have faccessat so we can simply use it.

function                                             old     new   delta
test_exec                                              -     125    +125
find_command                                         911     918      +7
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/0 up/down: 132/0)             Total: 132 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2024-10-07 05:46:31 +02:00
parent 748b168154
commit 860b3d066f
1 changed files with 51 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

54
shell/ash.c
View file

@ -491,6 +491,11 @@ struct globals_misc {
char **trap_ptr; /* used only by "trap hack" */
/* Rarely referenced stuff */
/* Cached supplementary group array (for testing executable'ity of files) */
int ngroups;
gid_t *group_array;
#if ENABLE_ASH_RANDOM_SUPPORT
random_t random_gen;
#endif
@ -523,6 +528,8 @@ extern struct globals_misc *BB_GLOBAL_CONST ash_ptr_to_globals_misc;
#define may_have_traps (G_misc.may_have_traps )
#define trap (G_misc.trap )
#define trap_ptr (G_misc.trap_ptr )
#define ngroups (G_misc.ngroups )
#define group_array (G_misc.group_array)
#define random_gen (G_misc.random_gen )
#define backgndpid (G_misc.backgndpid )
#define INIT_G_misc() do { \
@ -10171,6 +10178,7 @@ static int FAST_FUNC printfcmd(int argc, char **argv) { return printf_main(argc,
#endif
#if ENABLE_ASH_TEST || BASH_TEST2
static int FAST_FUNC testcmd(int argc, char **argv) { return test_main(argc, argv); }
// TODO: pass &ngroups and &group_array addresses to test_main to use cached supplementary groups
#endif
#if ENABLE_ASH_SLEEP
static int FAST_FUNC sleepcmd(int argc, char **argv) { return sleep_main(argc, argv); }
@ -13782,6 +13790,43 @@ readcmdfile(char *name)
/* ============ find_command inplementation */
static int test_exec(/*const char *fullname,*/ struct stat *statb)
{
/*
* TODO: use faccessat(AT_FDCWD, fullname, X_OK, AT_EACCESS)
* instead: executability may depend on ACLs, capabilities
* and who knows what else, not just mode bits.
* (faccessat2 syscall was added to Linux in May 14 2020)
*/
mode_t stmode;
uid_t euid;
enum { ANY_IX = S_IXUSR | S_IXGRP | S_IXOTH };
/* Do we already know with no extra syscalls? */
if (!S_ISREG(statb->st_mode))
return 0; /* not a regular file */
if ((statb->st_mode & ANY_IX) == 0)
return 0; /* no one can execute */
if ((statb->st_mode & ANY_IX) == ANY_IX)
return 1; /* anyone can execute */
/* Executability depends on our euid/egid/supplementary groups */
stmode = S_IXOTH;
euid = geteuid();
//TODO: cache euid?
if (euid == 0)
/* for root user, any X bit is good enough */
stmode = ANY_IX;
else if (statb->st_uid == euid)
stmode = S_IXUSR;
else if (statb->st_gid == getegid())
stmode = S_IXGRP;
else if (is_in_supplementary_groups(&ngroups, &group_array, statb->st_gid))
stmode = S_IXGRP;
return statb->st_mode & stmode;
}
/*
* Resolve a command name. If you change this routine, you may have to
* change the shellexec routine as well.
@ -13808,9 +13853,12 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
if (errno == EINTR)
continue;
#endif
absfail:
entry->cmdtype = CMDUNKNOWN;
return;
}
if (!test_exec(/*name,*/ &statb))
goto absfail;
}
entry->cmdtype = CMDNORMAL;
return;
@ -13923,9 +13971,6 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
e = errno;
goto loop;
}
e = EACCES; /* if we fail, this will be the error */
if (!S_ISREG(statb.st_mode))
continue;
if (lpathopt) { /* this is a %func directory */
stalloc(len);
/* NB: stalloc will return space pointed by fullname
@ -13938,6 +13983,9 @@ find_command(char *name, struct cmdentry *entry, int act, const char *path)
stunalloc(fullname);
goto success;
}
e = EACCES; /* if we fail, this will be the error */
if (!test_exec(/*fullname,*/ &statb))
continue;
TRACE(("searchexec \"%s\" returns \"%s\"\n", name, fullname));
if (!updatetbl) {
entry->cmdtype = CMDNORMAL;