[Valgrind-developers] [valgrind] Bug 506910 - openat2 with RESOLVE_NO_MAGICLINKS succeeds on /proc/self/exe

[Paul F. <pa...@so...>]

https://sourceware.org/cgit/valgrind/commit/?id=088ac305a2f27b4d8d5822bace59742719cc84d5

commit 088ac305a2f27b4d8d5822bace59742719cc84d5
Author: Paul Floyd <pj...@wa...>
Date:   Sat Jul 19 18:17:35 2025 +0200

    Bug 506910 - openat2 with RESOLVE_NO_MAGICLINKS succeeds on /proc/self/exe
    
    Previous change did most of the work but need to return without setting
    SfMayBlock. Add a testcase covering /proc/self/exe and /proc/PID/exe.

Diff:
---
 .gitignore                            |  1 +
 NEWS                                  |  1 +
 coregrind/m_syswrap/syswrap-generic.c |  1 +
 coregrind/m_syswrap/syswrap-linux.c   |  3 ++-
 none/tests/linux/Makefile.am          |  3 +++
 none/tests/linux/bug506910.cpp        | 44 +++++++++++++++++++++++++++++++++++
 none/tests/linux/bug506910.stderr.exp |  2 ++
 none/tests/linux/bug506910.vgtest     |  1 +
 8 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/.gitignore b/.gitignore
index 44454d08bb..0da54a7ebf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1885,6 +1885,7 @@
 /none/tests/linux/brk-overflow1
 /none/tests/linux/brk-overflow2
 /none/tests/linux/bug498317
+/none/tests/linux/bug506910
 /none/tests/linux/clonev
 /none/tests/linux/Makefile
 /none/tests/linux/Makefile.in
diff --git a/NEWS b/NEWS
index af88103641..29e2274eae 100644
--- a/NEWS
+++ b/NEWS
@@ -58,6 +58,7 @@ are not entered into bugzilla tend to get forgotten about or ignored.
 506499  Unhandled syscall 592 (exterrctl - FreeBSD
 506795  Better report which clone flags are problematic
 506928  Wrap (deprecated) linux specific ustat syscall
+506910  openat2 with RESOLVE_NO_MAGICLINKS succeeds on /proc/self/exe
 506930  valgrind allows SIGKILL being reset to SIG_DFL
 506970  mmap needs an EBADF fd_allowed check
 
diff --git a/coregrind/m_syswrap/syswrap-generic.c b/coregrind/m_syswrap/syswrap-generic.c
index 727766869f..280b1ccb6a 100644
--- a/coregrind/m_syswrap/syswrap-generic.c
+++ b/coregrind/m_syswrap/syswrap-generic.c
@@ -4693,6 +4693,7 @@ PRE(sys_open)
    if (proc_self_exe) {
       // do the syscall with VG_(resolved_exename)
       SET_STATUS_from_SysRes(VG_(do_syscall3)(SYSNO, (Word)VG_(resolved_exename), ARG2, ARG3));
+      return;
    }
 #endif // defined(VGO_linux)
 
diff --git a/coregrind/m_syswrap/syswrap-linux.c b/coregrind/m_syswrap/syswrap-linux.c
index e16d293cd0..d1cfdad69a 100644
--- a/coregrind/m_syswrap/syswrap-linux.c
+++ b/coregrind/m_syswrap/syswrap-linux.c
@@ -6095,6 +6095,7 @@ no_client_write:
 
       // do the syscall with VG_(resolved_exename)
       SET_STATUS_from_SysRes(VG_(do_syscall4)(SYSNO, ARG1, (Word)VG_(resolved_exename), ARG3, ARG4));
+      return;
    }
 
    /* Otherwise handle normally */
@@ -14093,9 +14094,9 @@ PRE(sys_openat2)
    }
 
    if (proc_self_exe) {
-
       // do the syscall with VG_(resolved_exename)
       SET_STATUS_from_SysRes(VG_(do_syscall4)(SYSNO, ARG1, (Word)VG_(resolved_exename), ARG3, ARG4));
+      return;
    }
 
    /* Otherwise handle normally */
diff --git a/none/tests/linux/Makefile.am b/none/tests/linux/Makefile.am
index c81ffff548..c20b2d2d01 100644
--- a/none/tests/linux/Makefile.am
+++ b/none/tests/linux/Makefile.am
@@ -8,6 +8,7 @@ EXTRA_DIST = \
 	brk-overflow1.stderr.exp brk-overflow1.vgtest \
 	brk-overflow2.stderr.exp brk-overflow2.vgtest \
 	bug498317.stderr.exp bug498317.supp bug498317.vgtest \
+	bug506910.stderr.exp bug506910.vgtest \
 	clonev.stdout.exp clonev.stderr.exp clonev.vgtest \
         membarrier.stderr.exp membarrier.vgtest \
 	mremap.stderr.exp mremap.stderr.exp-glibc27 mremap.stdout.exp \
@@ -26,6 +27,7 @@ check_PROGRAMS = \
 	brk-overflow1 \
 	brk-overflow2 \
 	bug498317 \
+	bug506910 \
 	clonev \
 	mremap \
 	mremap2 \
@@ -46,6 +48,7 @@ AM_CFLAGS   += $(AM_FLAG_M3264_PRI)
 AM_CXXFLAGS += $(AM_FLAG_M3264_PRI)
 
 # Special needs
+bug506910_SOURCES = bug506910.cpp
 clonev_LDADD = -lpthread
 open_client_SOURCES = open_client.cpp
 pthread_stack_LDADD = -lpthread
diff --git a/none/tests/linux/bug506910.cpp b/none/tests/linux/bug506910.cpp
new file mode 100644
index 0000000000..2dbadf56a2
--- /dev/null
+++ b/none/tests/linux/bug506910.cpp
@@ -0,0 +1,44 @@
+// For Bug 5056910
+// openat2 with RESOLVE_NO_MAGICLINKS succeeds on /proc/self/exe
+#include <fcntl.h>
+#include <cerrno>
+#include <stdexcept>
+#include <string>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <linux/openat2.h>
+
+int main(int argc, char** argv)
+{
+    auto pid = getpid();
+    auto ppe = std::string("/proc/") + std::to_string(pid) + "/exe";
+#if defined(SYS_openat2)
+   struct open_how oh = { .flags=O_RDONLY, .mode=0UL, .resolve=RESOLVE_NO_MAGICLINKS };
+   int res = syscall(SYS_openat2, AT_FDCWD, "/proc/self/exe", &oh, sizeof(oh));
+   if (-1 != res)
+   {
+      throw std::runtime_error("openat2 should have failed");
+   }
+   else
+   {
+      if (errno != ELOOP)
+      {
+         throw std::runtime_error("errno should be ELOOP");
+      }
+   }
+
+   res = syscall(SYS_openat2, AT_FDCWD, ppe.c_str(), &oh, sizeof(oh));
+   if (-1 != res)
+   {
+       throw std::runtime_error("openat2 should have failed");
+   }
+   else
+   {
+       if (errno != ELOOP)
+       {
+           throw std::runtime_error("errno should be ELOOP");
+       }
+   }
+#endif
+}
diff --git a/none/tests/linux/bug506910.stderr.exp b/none/tests/linux/bug506910.stderr.exp
new file mode 100644
index 0000000000..139597f9cb
--- /dev/null
+++ b/none/tests/linux/bug506910.stderr.exp
@@ -0,0 +1,2 @@
+
+
diff --git a/none/tests/linux/bug506910.vgtest b/none/tests/linux/bug506910.vgtest
new file mode 100644
index 0000000000..28e3f29751
--- /dev/null
+++ b/none/tests/linux/bug506910.vgtest
@@ -0,0 +1 @@
+prog: bug506910