From: Martin Cermak <mcermak@redhat.com>
Date: Tue, 5 Aug 2025 15:36:29 +0000 (+0200)
Subject: Make fchmodat and fchmodat2 syscall wrappers accept AT_FDCWD
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=90d4ed67ff52b859bf1f2d8cbea8816ca705d6f6;p=thirdparty%2Fvalgrind.git

Make fchmodat and fchmodat2 syscall wrappers accept AT_FDCWD

The fchmodat and fchmodat2 syscall wrappers should accept special
value AT_FDCWD as a valid file descriptor.

https://bugs.kde.org/show_bug.cgi?id=507873
---

diff --git a/NEWS b/NEWS
index cecbd6db7..6b21446ec 100644
--- a/NEWS
+++ b/NEWS
@@ -68,6 +68,7 @@ are not entered into bugzilla tend to get forgotten about or ignored.
 506967  Implement and override mallinfo2
 506970  mmap needs an EBADF fd_allowed check
 507173  s390x: Crash when constant folding is disabled
+507873  Make fchmodat and fchmodat2 syscall wrappers accept AT_FDCWD
 507897  Allow for patching LTP sources
 
 To see details of a given bug, visit
diff --git a/coregrind/m_syswrap/syswrap-linux.c b/coregrind/m_syswrap/syswrap-linux.c
index c81d941a7..96d22e6f4 100644
--- a/coregrind/m_syswrap/syswrap-linux.c
+++ b/coregrind/m_syswrap/syswrap-linux.c
@@ -6407,15 +6407,21 @@ POST(sys_readlinkat)
 
 PRE(sys_fchmodat)
 {
+   Int arg_1 = (Int) ARG1;
+   const HChar *path = (const HChar*) ARG2;
    FUSE_COMPATIBLE_MAY_BLOCK();
-   PRINT("sys_fchmodat ( %ld, %#" FMT_REGWORD "x(%s), %" FMT_REGWORD "u )",
-         SARG1, ARG2, (HChar*)(Addr)ARG2, ARG3);
+   PRINT("sys_fchmodat ( %d, %#" FMT_REGWORD "x(%s), %" FMT_REGWORD "u )",
+         arg_1, ARG2, path, ARG3);
    PRE_REG_READ3(long, "fchmodat",
                  int, dfd, const char *, path, vki_mode_t, mode);
    PRE_MEM_RASCIIZ( "fchmodat(path)", ARG2 );
-   if ( !ML_(fd_allowed)(SARG1, "fchmodat", tid, False) )
-     SET_STATUS_Failure( VKI_EBADF );
-
+   if (ML_(safe_to_deref) (path, 1)) {
+      // If pathname is relative and dirfd is the special value AT_FDCWD, then pathname is interpreted ...
+      if (path[0] != '/')
+         if ( arg_1 != VKI_AT_FDCWD && !ML_(fd_allowed)(arg_1, "fchmodat", tid, False) )
+            SET_STATUS_Failure( VKI_EBADF );
+      // If pathname is absolute, then dirfd is ignored
+   }
 }
 
 PRE(sys_cachestat)
@@ -6440,16 +6446,23 @@ POST(sys_cachestat)
 
 PRE(sys_fchmodat2)
 {
+   Int arg_1 = (Int) ARG1;
+   const HChar *path = (const HChar*) ARG2;
    FUSE_COMPATIBLE_MAY_BLOCK();
-   PRINT("sys_fchmodat2 ( %ld, %#" FMT_REGWORD "x(%s), %" FMT_REGWORD "u, %"
+   PRINT("sys_fchmodat2 ( %d, %#" FMT_REGWORD "x(%s), %" FMT_REGWORD "u, %"
 	  FMT_REGWORD "u )",
-         SARG1, ARG2, (HChar*)(Addr)ARG2, ARG3, ARG4);
+         arg_1, ARG2, path, ARG3, ARG4);
    PRE_REG_READ4(long, "fchmodat2",
                  int, dfd, const char *, path, vki_mode_t, mode,
                  unsigned int, flags);
    PRE_MEM_RASCIIZ( "fchmodat2(pathname)", ARG2 );
-   if ( !ML_(fd_allowed)(SARG1, "fchmodat2", tid, False) )
-     SET_STATUS_Failure( VKI_EBADF );
+   if (ML_(safe_to_deref) (path, 1)) {
+      // If pathname is relative and dirfd is the special value AT_FDCWD, then pathname is interpreted ...
+      if (path[0] != '/')
+          if ( arg_1 != VKI_AT_FDCWD && !ML_(fd_allowed)(arg_1, "fchmodat2", tid, False) )
+             SET_STATUS_Failure( VKI_EBADF );
+      // If pathname is absolute, then dirfd is ignored
+   }
 }
 
 PRE(sys_faccessat)