git: 8ae3f4499194 - main - system(3): Fix null case

The branch main has been updated by des:

URL: https://cgit.FreeBSD.org/src/commit/?id=8ae3f44991948cc97b09adc248a9a46db71bf9e0

commit 8ae3f44991948cc97b09adc248a9a46db71bf9e0
Author:     Dag-Erling Smørgrav <des@FreeBSD.org>
AuthorDate: 2026-02-25 21:12:42 +0000
Commit:     Dag-Erling Smørgrav <des@FreeBSD.org>
CommitDate: 2026-02-25 21:12:42 +0000

    system(3): Fix null case
    
    Our manual page states that if given a null pointer, system() returns
    non-zero if the shell is available and zero if it is not.  This is
    consistent with the C standard's description of system(), but it is not
    what we actually do.  What we actually do is always return non-zero, as
    required by POSIX.
    
    As the POSIX rationale explains, implementing the logic required by the
    C standard does not violate POSIX, since a conforming system always has
    a shell, therefore the logic will always return non-zero.
    
    Since our libc is commonly used in non-conforming situations such as
    chroots or thin jails, we should implement the full logic required by
    the C standard.
    
    MFC after:      1 week
    Sponsored by:   Klara, Inc.
    Reviewed by:    obiwac, bnovkov, kevans
    Differential Revision:  https://reviews.freebsd.org/D55484
---
 lib/libc/stdlib/system.c            |  2 +-
 lib/libc/tests/stdlib/system_test.c | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/lib/libc/stdlib/system.c b/lib/libc/stdlib/system.c
index 17dd63eb52f9..94f7460c9b68 100644
--- a/lib/libc/stdlib/system.c
+++ b/lib/libc/stdlib/system.c
@@ -64,7 +64,7 @@ __libc_system(const char *command)
 	pid_t pid;
 
 	if (command == NULL)			/* just checking... */
-		return (1);
+		return (eaccess(_PATH_BSHELL, X_OK) == 0);
 
 	/*
 	 * If we are the first concurrent instance, ignore SIGINT and
diff --git a/lib/libc/tests/stdlib/system_test.c b/lib/libc/tests/stdlib/system_test.c
index 713e4bb0f87a..b6a31583d52d 100644
--- a/lib/libc/tests/stdlib/system_test.c
+++ b/lib/libc/tests/stdlib/system_test.c
@@ -57,10 +57,20 @@ ATF_TC(system_null);
 ATF_TC_HEAD(system_null, tc)
 {
 	atf_tc_set_md_var(tc, "descr", "system(NULL)");
+	atf_tc_set_md_var(tc, "require.user", "root");
 }
 ATF_TC_BODY(system_null, tc)
 {
+	/* First, test in a normal environment */
 	ATF_REQUIRE_EQ(1, system(NULL));
+
+	/* Now enter an empty chroot */
+	ATF_REQUIRE_EQ(0, chroot("."));
+	ATF_REQUIRE_EQ(0, chdir("/"));
+
+	/* Test again with no shell available */
+	ATF_REQUIRE_EQ(0, system(NULL));
+	ATF_REQUIRE_EQ(W_EXITCODE(127, 0), system("true"));
 }
 
 /*