From 978ffcbf00d82b03b79e64b5c8249589b50e7463 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 8 Jan 2024 16:43:04 -0800 Subject: execve: open the executable file before doing anything else No point in allocating a new mm, counting arguments and environment variables etc if we're just going to return ENOENT. This patch does expose the fact that 'do_filp_open()' that execve() uses is still unnecessarily expensive in the failure case, because it allocates the 'struct file *' early, even if the path lookup (which is heavily optimized) fails. So that remains an unnecessary cost in the "no such executable" case, but it's a separate issue. Regardless, I do not want to do _both_ a filename_lookup() and a later do_filp_open() like the origin patch by Josh Triplett did in [1]. Reported-by: Josh Triplett Cc: Kees Cook Cc: Mateusz Guzik Cc: Al Viro Link: https://lore.kernel.org/lkml/5c7333ea4bec2fad1b47a8fa2db7c31e4ffc4f14.1663334978.git.josh@joshtriplett.org/ [1] Link: https://lore.kernel.org/lkml/202209161637.9EDAF6B18@keescook/ Link: https://lore.kernel.org/lkml/CAHk-=wgznerM-xs+x+krDfE7eVBiy_HOam35rbsFMMOwvYuEKQ@mail.gmail.com/ Link: https://lore.kernel.org/lkml/CAHk-=whf9qLO8ipps4QhmS0BkM8mtWJhvnuDSdtw5gFjhzvKNA@mail.gmail.com/ Signed-off-by: Linus Torvalds --- fs/exec.c | 69 ++++++++++++++++++++++++++++++++------------------------------- 1 file changed, 35 insertions(+), 34 deletions(-) (limited to 'fs/exec.c') diff --git a/fs/exec.c b/fs/exec.c index 73e4045df271..8cdd5b2dd09c 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1508,12 +1508,24 @@ static void free_bprm(struct linux_binprm *bprm) kfree(bprm); } -static struct linux_binprm *alloc_bprm(int fd, struct filename *filename) +static struct linux_binprm *alloc_bprm(int fd, struct filename *filename, int flags) { - struct linux_binprm *bprm = kzalloc(sizeof(*bprm), GFP_KERNEL); + struct linux_binprm *bprm; + struct file *file; int retval = -ENOMEM; - if (!bprm) - goto out; + + file = do_open_execat(fd, filename, flags); + if (IS_ERR(file)) + return ERR_CAST(file); + + bprm = kzalloc(sizeof(*bprm), GFP_KERNEL); + if (!bprm) { + allow_write_access(file); + fput(file); + return ERR_PTR(-ENOMEM); + } + + bprm->file = file; if (fd == AT_FDCWD || filename->name[0] == '/') { bprm->filename = filename->name; @@ -1526,18 +1538,28 @@ static struct linux_binprm *alloc_bprm(int fd, struct filename *filename) if (!bprm->fdpath) goto out_free; + /* + * Record that a name derived from an O_CLOEXEC fd will be + * inaccessible after exec. This allows the code in exec to + * choose to fail when the executable is not mmaped into the + * interpreter and an open file descriptor is not passed to + * the interpreter. This makes for a better user experience + * than having the interpreter start and then immediately fail + * when it finds the executable is inaccessible. + */ + if (get_close_on_exec(fd)) + bprm->interp_flags |= BINPRM_FLAGS_PATH_INACCESSIBLE; + bprm->filename = bprm->fdpath; } bprm->interp = bprm->filename; retval = bprm_mm_init(bprm); - if (retval) - goto out_free; - return bprm; + if (!retval) + return bprm; out_free: free_bprm(bprm); -out: return ERR_PTR(retval); } @@ -1807,10 +1829,8 @@ static int exec_binprm(struct linux_binprm *bprm) /* * sys_execve() executes a new program. */ -static int bprm_execve(struct linux_binprm *bprm, - int fd, struct filename *filename, int flags) +static int bprm_execve(struct linux_binprm *bprm) { - struct file *file; int retval; retval = prepare_bprm_creds(bprm); @@ -1826,26 +1846,8 @@ static int bprm_execve(struct linux_binprm *bprm, current->in_execve = 1; sched_mm_cid_before_execve(current); - file = do_open_execat(fd, filename, flags); - retval = PTR_ERR(file); - if (IS_ERR(file)) - goto out_unmark; - sched_exec(); - bprm->file = file; - /* - * Record that a name derived from an O_CLOEXEC fd will be - * inaccessible after exec. This allows the code in exec to - * choose to fail when the executable is not mmaped into the - * interpreter and an open file descriptor is not passed to - * the interpreter. This makes for a better user experience - * than having the interpreter start and then immediately fail - * when it finds the executable is inaccessible. - */ - if (bprm->fdpath && get_close_on_exec(fd)) - bprm->interp_flags |= BINPRM_FLAGS_PATH_INACCESSIBLE; - /* Set the unchanging part of bprm->cred */ retval = security_bprm_creds_for_exec(bprm); if (retval) @@ -1875,7 +1877,6 @@ out: if (bprm->point_of_no_return && !fatal_signal_pending(current)) force_fatal_sig(SIGSEGV); -out_unmark: sched_mm_cid_after_execve(current); current->fs->in_exec = 0; current->in_execve = 0; @@ -1910,7 +1911,7 @@ static int do_execveat_common(int fd, struct filename *filename, * further execve() calls fail. */ current->flags &= ~PF_NPROC_EXCEEDED; - bprm = alloc_bprm(fd, filename); + bprm = alloc_bprm(fd, filename, flags); if (IS_ERR(bprm)) { retval = PTR_ERR(bprm); goto out_ret; @@ -1959,7 +1960,7 @@ static int do_execveat_common(int fd, struct filename *filename, bprm->argc = 1; } - retval = bprm_execve(bprm, fd, filename, flags); + retval = bprm_execve(bprm); out_free: free_bprm(bprm); @@ -1984,7 +1985,7 @@ int kernel_execve(const char *kernel_filename, if (IS_ERR(filename)) return PTR_ERR(filename); - bprm = alloc_bprm(fd, filename); + bprm = alloc_bprm(fd, filename, 0); if (IS_ERR(bprm)) { retval = PTR_ERR(bprm); goto out_ret; @@ -2019,7 +2020,7 @@ int kernel_execve(const char *kernel_filename, if (retval < 0) goto out_free; - retval = bprm_execve(bprm, fd, filename, 0); + retval = bprm_execve(bprm); out_free: free_bprm(bprm); out_ret: -- cgit v1.2.3-59-g8ed1b