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open: Fix race condition when called with O_TRUNC

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Fix a race condition in which a file opened with O_TRUNC is made
available to other file functions expecting a file descriptor before
the truncation is performed.

This is only possible if the other thread was using an invalid file
descriptor as the open call has yet to finish.

Closes #5109
This commit is contained in:
Loris Nardo
2024-07-27 18:40:23 +02:00
committed by Kinsey Moore
parent 7440264601
commit 9c57576a4b
1 changed files with 13 additions and 3 deletions
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16
cpukit/libcsupport/src/open.c
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@@ -142,16 +142,26 @@ static int do_open(
rv = (*iop->pathinfo.handlers->open_h)( iop, path, oflag, mode );
if ( rv == 0 ) {
rtems_libio_iop_flags_set( iop, LIBIO_FLAGS_OPEN );
/*
* Postpone the setting of LIBIO_FLAGS_OPEN after the truncation of the
* file, this ensures that the file descriptor cannot be used or closed
* during or just before the truncation by some other thread.
*/
if ( truncate ) {
rv = ftruncate( fd, 0 );
if ( write_access ) {
rv = (*iop->pathinfo.handlers->ftruncate_h)( iop, 0 );
} else {
rv = -1;
errno = EINVAL;
}
if ( rv != 0 ) {
(*iop->pathinfo.handlers->close_h)( iop );
}
}
if ( rv == 0 ) {
rtems_libio_iop_flags_set( iop, LIBIO_FLAGS_OPEN );
rv = fd;
} else {
rv = -1;