libsparse: fix double free after block splitting
Due to https://r.android.com/1310496, sparse_file_write() splits all
blocks larger than 64 MiB. However, the code that splits file-backed
blocks copies the pointer to the filename without duplicating the
underlying memory, causing a double free in backed_block_destroy()
later. Fix this by using strdup(). Also, as long as that is being
fixed, also check for failure.
Test: SANITIZE_HOST=address mmm external/e2fsprogs
mkdir mnt
mkfs.ext4 img 1G
sudo mount img mnt
sudo cp /dev/urandom mnt/file
sudo umount mnt
ext2simg img simg
Before this fix it gave:
==2216498==ERROR: AddressSanitizer: attempting double-free on 0x602000000090 in thread T0:
#0 0x55a52454c9a2 in free out/stage2/runtimes/runtimes-x86_64-unknown-linux-gnu-bins/out/llvm-project/compiler-rt/lib/asan/asan_malloc_linux.cpp:52:3
#1 0x7ffa247c82ee in backed_block_destroy(backed_block*) system/core/libsparse/backed_block.cpp:106:5
#2 0x7ffa247c82ee in backed_block_list_destroy(backed_block_list*) system/core/libsparse/backed_block.cpp:124:7
#3 0x7ffa247cd055 in sparse_file_destroy system/core/libsparse/sparse.cpp:49:3
#4 0x55a524587b75 in main external/e2fsprogs/contrib/android/ext2simg.c:239:2
Change-Id: I4607ef5adcf6512645342beaf91aff6033414e54
diff --git a/libsparse/backed_block.cpp b/libsparse/backed_block.cpp
index 6229e7c..a0d1cde 100644
--- a/libsparse/backed_block.cpp
+++ b/libsparse/backed_block.cpp
@@ -315,6 +315,10 @@
bb->len = len;
bb->type = BACKED_BLOCK_FILE;
bb->file.filename = strdup(filename);
+ if (!bb->file.filename) {
+ free(bb);
+ return -ENOMEM;
+ }
bb->file.offset = offset;
bb->next = nullptr;
@@ -359,14 +363,17 @@
new_bb->len = bb->len - max_len;
new_bb->block = bb->block + max_len / bbl->block_size;
new_bb->next = bb->next;
- bb->next = new_bb;
- bb->len = max_len;
switch (bb->type) {
case BACKED_BLOCK_DATA:
new_bb->data.data = (char*)bb->data.data + max_len;
break;
case BACKED_BLOCK_FILE:
+ new_bb->file.filename = strdup(bb->file.filename);
+ if (!new_bb->file.filename) {
+ free(new_bb);
+ return -ENOMEM;
+ }
new_bb->file.offset += max_len;
break;
case BACKED_BLOCK_FD:
@@ -376,5 +383,7 @@
break;
}
+ bb->next = new_bb;
+ bb->len = max_len;
return 0;
}