utils-std

commit: 4036111e8cb961d05bc5aefa4e72b25739339874
parent 8ea6e9f38d660dcc920717b6944b85fa669d562f
Author: Haelwenn (lanodan) Monnier <contact@hacktivis.me>
Date:   Sat, 28 Jun 2025 05:11:48 +0200

cmd/df: use reallocarray instead of hardcoding a maximum of 4096 devices

Diffstat:
M
cmd/df.c
51
++++++++++++++++++++++++++++++++++++++++++---------
M
configure
4
++--

2 files changed, 44 insertions(+), 11 deletions(-)
diff --git a/cmd/df.c b/cmd/df.c
@@ -2,9 +2,10 @@
 // SPDX-FileCopyrightText: 2017 Haelwenn (lanodan) Monnier <contact+utils@hacktivis.me>
 // SPDX-License-Identifier: MPL-2.0
 
-#define _POSIX_C_SOURCE 200809L
+#define _POSIX_C_SOURCE 202405L
 #define _DEFAULT_SOURCE // mntent in glibc 2.19+
 
+#include "../lib/reallocarray.h"
 #include "../libutils/getopt_nolong.h"
 #include "../libutils/humanize.h"
 
@@ -53,6 +54,7 @@ main(int argc, char *argv[])
 {
 	bool opt_P = false, opt_h = false, opt_a = false, opt_T = false, opt_l = false, opt_i = false;
 	int fs_col_width = 20;
+	dev_t *devices = NULL;
 
 	size_t excluded_count = 0;
 	static char *excluded[DF_MNT_TYPE_MAX];
@@ -212,9 +214,25 @@ main(int argc, char *argv[])
 		goto error;
 	}
 
-	// FIXME: Fix maximum number of mount entries / devices
-	dev_t devices[4096];
+	// Linux has a configurable limit of maximum mounts which defaults to 100_000
+	// See /proc/sys/fs/mount-max introduced in Linux 4.9 for CVE-2016-6213
+	// https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d29216842a85c7970c536108e093963f02714498
+	//
+	// Which is way too much to be either stack-allocated or statically allocated:
+	// 100000*sizeof(dev_t) = 100000*8 bytes ≈ 781.25 KiB
+	// So reallocarray to the rescue
 	size_t devices_found = 0;
+	size_t devices_len = 100;
+	devices = reallocarray(NULL, devices_len, sizeof(dev_t));
+	if(!devices)
+	{
+		fprintf(stderr,
+		        "%s: error: Failed to allocate memory for storing (%zd) devices: %s\n",
+		        argv0,
+		        devices_len,
+		        strerror(errno));
+		goto error;
+	}
 
 	// Even with argc>0 we still need to go over mntent for the filesystem mountpoint and type
 	while(args_left > 0)
@@ -305,10 +323,23 @@ main(int argc, char *argv[])
 
 			if(dupe) continue;
 
-			if(devices_found >= 4096)
-				fprintf(stderr,
-				        "%s: warning: Reached maximum amount of devices which can be deduplicated\n",
-				        argv0);
+			if(devices_found + 1 >= devices_len)
+			{
+				devices_len *= 2;
+				if(devices_len <= 0) abort();
+
+				devices = reallocarray(devices, devices_len, sizeof(dev_t));
+
+				if(!devices)
+				{
+					fprintf(stderr,
+					        "%s: error: Failed to allocate memory for storing (%zd) devices: %s\n",
+					        argv0,
+					        devices_len,
+					        strerror(errno));
+					goto error;
+				}
+			}
 
 			devices[devices_found++] = file_stats.st_dev;
 		}
@@ -431,12 +462,14 @@ main(int argc, char *argv[])
 
 	endmntent(mounted);
 
-	if(argc > 0) free(arg_devs);
+	free(devices);
+	free(arg_devs);
 
 	return 0;
 
 error:
-	if(argc > 0) free(arg_devs);
+	free(devices);
+	free(arg_devs);
 
 	return 1;
 }
diff --git a/configure b/configure
@@ -249,8 +249,8 @@ check_conftest configure.d/sendfile_linux.c && cpp_define HAS_SENDFILE
 check_conftest configure.d/copy_file_range.c && cpp_define HAS_COPY_FILE_RANGE
 
 if ! check_conftest configure.d/reallocarray.c; then
-	echo 'Disabling cmd/tr cmd/cut cmd/join'
-	target_filter="${target_filter} -e cmd/tr. -e cmd/cut. -e cmd/join."
+	echo 'Disabling cmd/df cmd/tr cmd/cut cmd/join'
+	target_filter="${target_filter} -e cmd/df. -e cmd/tr. -e cmd/cut. -e cmd/join."
 fi
 
 check_conftest configure.d/getopt_long.c && cpp_define HAS_GETOPT_LONG