[PATCH] git-p4: avoid shell interpretation of commit ids in applyCommit

["Anupam Mediratta via GitGitGadget" <gitgitgadget@gmail.com>]

From: Anupam Mediratta <mediratta@gmail.com>

applyCommit() builds a `git diff-tree ... | git apply ...` pipeline as a
shell command string, interpolating the commit id and running it via
os.system()/system(shell=True). The id usually comes from `git rev-list`
output (safe, plain SHA-1s), but it can also come verbatim from the
user-supplied `--commit` option, which is never validated
(git-p4.py:2620-2631). A value such as `$(some-command)` passed to
`--commit` is executed by the shell during command substitution, even
though the value is wrapped in double quotes.

Replace the shell pipeline with two argument-vector subprocess calls
connected directly through a pipe, matching the pattern already used
throughout this file (read_pipe, read_pipe_lines, p4_system). This
removes the shell entirely, rather than relying on quoting the
interpolated value.

Add a regression test exercising `git p4 submit --commit` with a shell
metacharacter payload, verifying it is never interpreted.

Signed-off-by: Anupam Mediratta <mediratta@gmail.com>
---
    git-p4: avoid shell interpretation of commit ids in applyCommit
    
    P4Submit.applyCommit() builds a git diff-tree | git apply pipeline as a
    shell command string and runs it with os.system()/system(shell=True).
    The commit id it interpolates is usually a plain SHA-1 from git
    rev-list, but it can also come straight from the unvalidated --commit
    command-line option, so a value such as $(some-command) passed to
    --commit gets executed by the shell during command substitution.
    
    This replaces the shell pipeline with two argument-vector subprocess
    calls connected directly through a pipe, the same pattern already used
    everywhere else in this file (read_pipe, read_pipe_lines, p4_system), so
    there's no shell left to escape correctly. It also adds a regression
    test in t9803 that submits a commit id crafted with shell metacharacters
    and checks they're never executed.
    
    I have read https://git-scm.com/docs/SubmittingPatches#ai and confirm
    this contribution complies with it.
    
    Changes since v1: corrected the description of the affected data (it's
    the unvalidated --commit argument, not Perforce server data, that was
    ever exploitable here), removed the shell entirely instead of quoting
    the interpolated value, replaced a test that never reached the
    vulnerable code with one that drives it through git p4 submit --commit,
    and fixed the commit message format (subsystem prefix, rationale,
    sign-off).

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2411%2Fanupamme%2Ffix-repo-git-git-p4-cwe-78-shell-injection-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2411/anupamme/fix-repo-git-git-p4-cwe-78-shell-injection-v1
Pull-Request: https://github.com/git/git/pull/2411

 git-p4.py                         | 31 +++++++++++++++++++++----------
 t/t9803-git-p4-shell-metachars.sh | 16 ++++++++++++++++
 2 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/git-p4.py b/git-p4.py
index c0ca7becaf..b09f5cd740 100755
--- a/git-p4.py
+++ b/git-p4.py
@@ -465,6 +465,22 @@ def p4_system(cmd, *k, **kw):
         raise subprocess.CalledProcessError(retcode, real_cmd)
 
 
+def diffTreeApply(id, applyArgs):
+    """Pipe `git diff-tree --full-index -p <id>` into `git apply <applyArgs>`
+    without a shell, so id can never be interpreted as shell syntax. Returns
+    the exit status of git apply."""
+    diffArgv = ["git", "diff-tree", "--full-index", "-p", id]
+    applyArgv = ["git", "apply"] + applyArgs
+    if verbose:
+        print("TryPatch: %s | %s" % (" ".join(diffArgv), " ".join(applyArgv)))
+    diffProc = subprocess.Popen(diffArgv, stdout=subprocess.PIPE)
+    applyProc = subprocess.Popen(applyArgv, stdin=diffProc.stdout)
+    diffProc.stdout.close()
+    applyProc.wait()
+    diffProc.wait()
+    return applyProc.returncode
+
+
 def die_bad_access(s):
     die("failure accessing depot: {0}".format(s.rstrip()))
 
@@ -2234,16 +2250,11 @@ class P4Submit(Command, P4UserMap):
             else:
                 die("unknown modifier %s for %s" % (modifier, path))
 
-        diffcmd = "git diff-tree --full-index -p \"%s\"" % (id)
-        patchcmd = diffcmd + " | git apply "
-        tryPatchCmd = patchcmd + "--check -"
-        applyPatchCmd = patchcmd + "--check --apply -"
+        tryPatchArgs = ["--check", "-"]
+        applyPatchArgs = ["--check", "--apply", "-"]
         patch_succeeded = True
 
-        if verbose:
-            print("TryPatch: %s" % tryPatchCmd)
-
-        if os.system(tryPatchCmd) != 0:
+        if diffTreeApply(id, tryPatchArgs) != 0:
             fixed_rcs_keywords = False
             patch_succeeded = False
             print("Unfortunately applying the change failed!")
@@ -2279,7 +2290,7 @@ class P4Submit(Command, P4UserMap):
 
             if fixed_rcs_keywords:
                 print("Retrying the patch with RCS keywords cleaned up")
-                if os.system(tryPatchCmd) == 0:
+                if diffTreeApply(id, tryPatchArgs) == 0:
                     patch_succeeded = True
                     print("Patch succeesed this time with RCS keywords cleaned")
 
@@ -2291,7 +2302,7 @@ class P4Submit(Command, P4UserMap):
         #
         # Apply the patch for real, and do add/delete/+x handling.
         #
-        system(applyPatchCmd, shell=True)
+        diffTreeApply(id, applyPatchArgs)
 
         for f in filesToChangeType:
             p4_edit(f, "-t", "auto")
diff --git a/t/t9803-git-p4-shell-metachars.sh b/t/t9803-git-p4-shell-metachars.sh
index 2913277013..ef8fd6e094 100755
--- a/t/t9803-git-p4-shell-metachars.sh
+++ b/t/t9803-git-p4-shell-metachars.sh
@@ -105,4 +105,20 @@ test_expect_success 'branch with shell char' '
 	)
 '
 
+test_expect_success 'git p4 submit --commit does not execute shell metachars in commit id' '
+	git p4 clone --dest="$git" //depot &&
+	test_when_finished cleanup_git &&
+	(
+		cd "$git" &&
+		git config git-p4.skipSubmitEditCheck true &&
+		echo f3 >file3 &&
+		git add file3 &&
+		git commit -m "add file3" &&
+		name='"'"'$(touch${IFS}injection-marker)'"'"' &&
+		git branch "$name" HEAD &&
+		P4EDITOR="test-tool chmtime +5" git p4 submit --commit "$name"
+	) &&
+	test_path_is_missing "$cli/injection-marker"
+'
+
 test_done

base-commit: d38352cd43ab9745686d697872408bc3249a153f
-- 
gitgitgadget