[PATCH] core-dumping unreadable binaries via PT_INTERP

Proposed patch to fix #5 in
http://www.isec.pl/vulnerabilities/isec-0017-binfmt_elf.txt
aka
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2004-1073

To reproduce, do
* grab poc at the end of advisory.
* add line "eph.p_memsz = 4096;" after "eph.p_filesz = 4096;"
  where first "4096" is something equal to or greater than 4096.
* ./poc /usr/bin/sudo && ls -l

Here I get with 2.6.20-rc5:

 -rw------- 1 ad   ad   102400 2007-01-15 19:17 core
 ---s--x--x 2 root root 101820 2007-01-15 19:15 /usr/bin/sudo

Check for MAY_READ like binfmt_misc.c does.

Signed-off-by: Alexey Dobriyan <adobriyan@openvz.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 17 insertions, 0 deletions

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 90461f49e902..669dbe5b0317 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -682,6 +682,15 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
                         retval = PTR_ERR(interpreter);
                         if (IS_ERR(interpreter))
                                 goto out_free_interp;
+
+                        /*
+                         * If the binary is not readable then enforce
+                         * mm->dumpable = 0 regardless of the interpreter's
+                         * permissions.
+                         */
+                        if (file_permission(interpreter, MAY_READ) < 0)
+                                bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
+
                         retval = kernel_read(interpreter, 0, bprm->buf,
                                              BINPRM_BUF_SIZE);
                         if (retval != BINPRM_BUF_SIZE) {
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 6e6d4568d548..a4d933a51208 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -234,6 +234,14 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm,
                                 goto error;
                         }
 
+                        /*
+                         * If the binary is not readable then enforce
+                         * mm->dumpable = 0 regardless of the interpreter's
+                         * permissions.
+                         */
+                        if (file_permission(interpreter, MAY_READ) < 0)
+                                bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
+
                         retval = kernel_read(interpreter, 0, bprm->buf,
                                              BINPRM_BUF_SIZE);
                         if (retval < 0)