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Kernel+Userland: Add symlink() syscall and add "-s" flag to /bin/ln.

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It's now possible to create symbolic links! :^)

This exposed an issue in Ext2FS where we'd write uninitialized data past
the end of an inode's content. Fix this by zeroing out the tail end of
the last block in a file.
This commit is contained in:
Andreas Kling 2019-03-02 01:50:34 +01:00
parent 37f6844c6c
commit 2c5a378ccc
10 changed files with 106 additions and 12 deletions
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38
Kernel/Ext2FileSystem.cpp
View file

@ -13,6 +13,8 @@
//#define EXT2_DEBUG
static const ssize_t max_inline_symlink_length = 60;
Retained<Ext2FS> Ext2FS::create(Retained<DiskDevice>&& device)
{
return adopt(*new Ext2FS(move(device)));
@ -437,10 +439,9 @@ ssize_t Ext2FSInode::read_bytes(off_t offset, ssize_t count, byte* buffer, FileD
// Symbolic links shorter than 60 characters are store inline inside the i_block array.
// This avoids wasting an entire block on short links. (Most links are short.)
static const unsigned max_inline_symlink_length = 60;
if (is_symlink() && size() < max_inline_symlink_length) {
ssize_t nread = min((off_t)size() - offset, static_cast<off_t>(count));
memcpy(buffer, m_raw_inode.i_block + offset, (size_t)nread);
memcpy(buffer, ((byte*)m_raw_inode.i_block) + offset, (size_t)nread);
return nread;
}
@ -495,13 +496,24 @@ ssize_t Ext2FSInode::read_bytes(off_t offset, ssize_t count, byte* buffer, FileD
ssize_t Ext2FSInode::write_bytes(off_t offset, ssize_t count, const byte* data, FileDescriptor*)
{
ASSERT(offset >= 0);
ASSERT(count >= 0);
Locker inode_locker(m_lock);
Locker fs_locker(fs().m_lock);
// FIXME: Support writing to symlink inodes.
ASSERT(!is_symlink());
ASSERT(offset >= 0);
if (is_symlink()) {
if ((offset + count) < max_inline_symlink_length) {
#ifdef EXT2_DEBUG
dbgprintf("Ext2FSInode: write_bytes poking into i_block array for inline symlink '%s' (%u bytes)\n", String((const char*)data, count).characters(), count);
#endif
memcpy(((byte*)m_raw_inode.i_block) + offset, data, (size_t)count);
if ((offset + count) > m_raw_inode.i_size)
m_raw_inode.i_size = offset + count;
set_metadata_dirty(true);
return count;
}
}
const ssize_t block_size = fs().block_size();
size_t old_size = size();
@ -528,6 +540,8 @@ ssize_t Ext2FSInode::write_bytes(off_t offset, ssize_t count, const byte* data,
dword offset_into_first_block = offset % block_size;
dword last_logical_block_index_in_file = size() / block_size;
ssize_t nwritten = 0;
size_t remaining_count = min((off_t)count, (off_t)new_size - offset);
const byte* in = data;
@ -542,7 +556,7 @@ ssize_t Ext2FSInode::write_bytes(off_t offset, ssize_t count, const byte* data,
size_t num_bytes_to_copy = min((size_t)block_size - offset_into_block, remaining_count);
ByteBuffer block;
if (offset_into_block != 0) {
if (offset_into_block != 0 || num_bytes_to_copy != block_size) {
block = fs().read_block(block_list[bi]);
if (!block) {
kprintf("Ext2FSInode::write_bytes: read_block(%u) failed (lbi: %u)\n", block_list[bi], bi);
@ -552,8 +566,14 @@ ssize_t Ext2FSInode::write_bytes(off_t offset, ssize_t count, const byte* data,
block = buffer_block;
memcpy(block.pointer() + offset_into_block, in, num_bytes_to_copy);
if (offset_into_block == 0 && !num_bytes_to_copy)
memset(block.pointer() + num_bytes_to_copy, 0, block_size - num_bytes_to_copy);
if (bi == last_logical_block_index_in_file && num_bytes_to_copy < block_size) {
size_t padding_start = new_size % block_size;
size_t padding_bytes = block_size - padding_start;
#ifdef EXT2_DEBUG
dbgprintf("Ext2FSInode::write_bytes padding last block of file with zero x %u (new_size=%u, offset_into_block=%u, num_bytes_to_copy=%u)\n", padding_bytes, new_size, offset_into_block, num_bytes_to_copy);
#endif
memset(block.pointer() + padding_start, 0, padding_bytes);
}
#ifdef EXT2_DEBUG
dbgprintf("Ext2FSInode::write_bytes: writing block %u (offset_into_block: %u)\n", block_list[bi], offset_into_block);
#endif