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Fix seek undefined behavior on signed integer overflow #1027

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Dec 6, 2024
Merged

Fix seek undefined behavior on signed integer overflow #1027

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f1c430e
Added some tests around seek integer overflow/underflow
geky Sep 24, 2024
abaec45
Fixed seek undefined behavior on signed integer overflow
geky Sep 24, 2024
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16 changes: 5 additions & 11 deletions lfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3664,22 +3664,16 @@ static lfs_ssize_t lfs_file_write_(lfs_t *lfs, lfs_file_t *file,
static lfs_soff_t lfs_file_seek_(lfs_t *lfs, lfs_file_t *file,
lfs_soff_t off, int whence) {
// find new pos
//
// fortunately for us, littlefs is limited to 31-bit file sizes, so we
// don't have to worry too much about integer overflow
lfs_off_t npos = file->pos;
if (whence == LFS_SEEK_SET) {
npos = off;
} else if (whence == LFS_SEEK_CUR) {
if ((lfs_soff_t)file->pos + off < 0) {
return LFS_ERR_INVAL;
} else {
npos = file->pos + off;
}
npos = file->pos + (lfs_off_t)off;
} else if (whence == LFS_SEEK_END) {
lfs_soff_t res = lfs_file_size_(lfs, file) + off;
if (res < 0) {
return LFS_ERR_INVAL;
} else {
npos = res;
}
npos = (lfs_off_t)lfs_file_size_(lfs, file) + (lfs_off_t)off;
}

if (npos > lfs->file_max) {
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108 changes: 108 additions & 0 deletions tests/test_seek.toml
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Expand Up @@ -405,3 +405,111 @@ code = '''
lfs_file_close(&lfs, &file) => 0;
lfs_unmount(&lfs) => 0;
'''


# test possible overflow/underflow conditions
#
# note these need -fsanitize=undefined to consistently detect
# overflow/underflow conditions

[cases.test_seek_filemax]
code = '''
lfs_t lfs;
lfs_format(&lfs, cfg) => 0;
lfs_mount(&lfs, cfg) => 0;
lfs_file_t file;
lfs_file_open(&lfs, &file, "kitty",
LFS_O_WRONLY | LFS_O_CREAT | LFS_O_APPEND) => 0;
uint8_t buffer[1024];
strcpy((char*)buffer, "kittycatcat");
size_t size = strlen((char*)buffer);
lfs_file_write(&lfs, &file, buffer, size) => size;

// seek with LFS_SEEK_SET
lfs_file_seek(&lfs, &file, LFS_FILE_MAX, LFS_SEEK_SET) => LFS_FILE_MAX;

// seek with LFS_SEEK_CUR
lfs_file_seek(&lfs, &file, 0, LFS_SEEK_CUR) => LFS_FILE_MAX;

// the file hasn't changed size, so seek end takes us back to the offset=0
lfs_file_seek(&lfs, &file, +10, LFS_SEEK_END) => size+10;

lfs_file_close(&lfs, &file) => 0;
lfs_unmount(&lfs) => 0;
'''

[cases.test_seek_underflow]
code = '''
lfs_t lfs;
lfs_format(&lfs, cfg) => 0;
lfs_mount(&lfs, cfg) => 0;
lfs_file_t file;
lfs_file_open(&lfs, &file, "kitty",
LFS_O_WRONLY | LFS_O_CREAT | LFS_O_APPEND) => 0;
uint8_t buffer[1024];
strcpy((char*)buffer, "kittycatcat");
size_t size = strlen((char*)buffer);
lfs_file_write(&lfs, &file, buffer, size) => size;

// underflow with LFS_SEEK_CUR, should error
lfs_file_seek(&lfs, &file, -(size+10), LFS_SEEK_CUR) => LFS_ERR_INVAL;
lfs_file_seek(&lfs, &file, -LFS_FILE_MAX, LFS_SEEK_CUR) => LFS_ERR_INVAL;
lfs_file_seek(&lfs, &file, -(size+LFS_FILE_MAX), LFS_SEEK_CUR)
=> LFS_ERR_INVAL;

// underflow with LFS_SEEK_END, should error
lfs_file_seek(&lfs, &file, -(size+10), LFS_SEEK_END) => LFS_ERR_INVAL;
lfs_file_seek(&lfs, &file, -LFS_FILE_MAX, LFS_SEEK_END) => LFS_ERR_INVAL;
lfs_file_seek(&lfs, &file, -(size+LFS_FILE_MAX), LFS_SEEK_END)
=> LFS_ERR_INVAL;

// file pointer should not have changed
lfs_file_tell(&lfs, &file) => size;

lfs_file_close(&lfs, &file) => 0;
lfs_unmount(&lfs) => 0;
'''

[cases.test_seek_overflow]
code = '''
lfs_t lfs;
lfs_format(&lfs, cfg) => 0;
lfs_mount(&lfs, cfg) => 0;
lfs_file_t file;
lfs_file_open(&lfs, &file, "kitty",
LFS_O_WRONLY | LFS_O_CREAT | LFS_O_APPEND) => 0;
uint8_t buffer[1024];
strcpy((char*)buffer, "kittycatcat");
size_t size = strlen((char*)buffer);
lfs_file_write(&lfs, &file, buffer, size) => size;

// seek to LFS_FILE_MAX
lfs_file_seek(&lfs, &file, LFS_FILE_MAX, LFS_SEEK_SET) => LFS_FILE_MAX;

// overflow with LFS_SEEK_CUR, should error
lfs_file_seek(&lfs, &file, +10, LFS_SEEK_CUR) => LFS_ERR_INVAL;
lfs_file_seek(&lfs, &file, +LFS_FILE_MAX, LFS_SEEK_CUR) => LFS_ERR_INVAL;

// LFS_SEEK_SET/END don't care about the current file position, but we can
// still overflow with a large offset

// overflow with LFS_SEEK_SET, should error
lfs_file_seek(&lfs, &file,
+((uint32_t)LFS_FILE_MAX+10),
LFS_SEEK_SET) => LFS_ERR_INVAL;
lfs_file_seek(&lfs, &file,
+((uint32_t)LFS_FILE_MAX+(uint32_t)LFS_FILE_MAX),
LFS_SEEK_SET) => LFS_ERR_INVAL;

// overflow with LFS_SEEK_END, should error
lfs_file_seek(&lfs, &file, +(LFS_FILE_MAX-size+10), LFS_SEEK_END)
=> LFS_ERR_INVAL;
lfs_file_seek(&lfs, &file, +(LFS_FILE_MAX-size+LFS_FILE_MAX), LFS_SEEK_END)
=> LFS_ERR_INVAL;

// file pointer should not have changed
lfs_file_tell(&lfs, &file) => LFS_FILE_MAX;

lfs_file_close(&lfs, &file) => 0;
lfs_unmount(&lfs) => 0;
'''
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