splatink/lbmk
1
0
Fork 0
mirror of https://codeberg.org/libreboot/lbmk.git synced 2026-03-25 13:29:03 +02:00
Code Issues Packages Projects Releases Wiki Activity

util/nvmutil: partially mitigate fd offset race

Browse Source 
our fallback pwrite/pread behaviour still does not
properly replicate the safety of real pwrite/pread

i intend to put this i/o code into a library for use
in other programs; nvmutil is single-threaded so
this change is largely redundant (but can't hurt)

Signed-off-by: Leah Rowe <leah@libreboot.org>
This commit is contained in:
Leah Rowe
2026-03-14 22:11:32 +00:00
parent d66ba5f781
commit f229c722a9
1 changed files with 42 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

54
util/nvmutil/nvmutil.c
View File

@@ -1951,6 +1951,7 @@ prw(int fd, void *mem, size_t nrw,
int saved_errno;
int positional_rw;
struct stat st;
off_t verified;
if (mem == NULL)
goto err_prw;
@@ -2014,22 +2015,51 @@ real_pread_pwrite:
goto real_pread_pwrite;
#else
if ((off_orig = lseek_loop(fd, (off_t)0, SEEK_CUR,
loop_eagain, loop_eintr)) == (off_t)-1)
loop_eagain, loop_eintr)) == (off_t)-1) {
r = -1;
else if (lseek_loop(fd, off, SEEK_SET,
loop_eagain, loop_eintr) == (off_t)-1)
} else if (lseek_loop(fd, off, SEEK_SET,
loop_eagain, loop_eintr) == (off_t)-1) {
r = -1;
} else {
verified = lseek_loop(fd, (off_t)0, SEEK_CUR,
loop_eagain, loop_eintr);
do {
if (rw_type == IO_PREAD)
r = read(fd, mem, nrw);
else if (rw_type == IO_PWRITE)
r = write(fd, mem, nrw);
/*
* Partial thread-safety: detect
* if the offset changed to what
* we previously got. If it did,
* then another thread may have
* changed it.
*
* This is no substitute for real
* pread/pwrite, which would be
* fully atomic at kernel-level
* and do not use file offsets.
*
* TODO: Add a toggle to make it
* recover instead, reset
* to known offset, and
* carry on operations.
*
* Failure is the better option
* here, since recovery would
* mask hidden bugs in code.
*/
if (off != verified)
goto err_prw;
r = rw_over_nrw(r, nrw);
} while (r == -1 &&
(errno == try_err(loop_eintr, EINTR)
|| errno == try_err(loop_eagain, EAGAIN)));
do {
if (rw_type == IO_PREAD)
r = read(fd, mem, nrw);
else if (rw_type == IO_PWRITE)
r = write(fd, mem, nrw);
r = rw_over_nrw(r, nrw);
} while (r == -1 &&
(errno == try_err(loop_eintr, EINTR)
|| errno == try_err(loop_eagain, EAGAIN)));
}
saved_errno = errno;
off_last = lseek_loop(fd, off_orig, SEEK_SET,