This bug was initially created as a copy of Bug #1855979

I am copying this bug because: 

Also applies to RHEL8

Description of problem:

When syncing using "--append" and the file on the sender is > 2GB and gets truncated between rsync receiving the checksum and the actual transfer, rsync dies in Segmentation Fault.
This is due to having the "n" computation on line 108 below wrap (it's supposed to be a int32):
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
105 static void matched(int f, struct sum_struct *s, struct map_struct *buf,
106                     OFF_T offset, int32 i)
107 {
108         int32 n = (int32)(offset - last_match); /* max value: block_size (int32) */
109         int32 j;
 :
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------


Version-Release number of selected component (if applicable):

rsync-3.1.2 and rsync-3.1.3 (RHEL8)

How reproducible:

ALWAYS


Steps to Reproduce: notes: line numbers in reproducer are from RHEL8's rsync ...

1. Create 2 >2GB big files, sent file /root/file and received file /mnt/file, with /mnt/file < /root/file

# truncate -s 2760M /root/file
# truncate -s 2759M /mnt/file

2. Start rsync to sync /root/file -> /mnt under GDB, with a breakpoint on "receive_sums"

# gdb --args /usr/bin/rsync --append -vvvv /root/file /mnt
[...]
(gdb) break receive_sums
(gdb) run

3. At breakpoint, hit "next" until the checksum is computed (hence the -vvvv mode) but before /root/file gets opened for transfer

Breakpoint 1, receive_sums (f=5) at sender.c:332
332			if (!(s = receive_sums(f_in))) {
(gdb) next
71		if (!(s = new(struct sum_struct)))
(gdb) 
74		read_sum_head(f, s);
(gdb) 
76		s->sums = NULL;
(gdb) 
78		if (DEBUG_GTE(DELTASUM, 3)) {
(gdb) 
send_files (f_in=5, f_out=<optimized out>) at sender.c:332
332			if (!(s = receive_sums(f_in))) {
(gdb) 
count=53790 n=53784 rem=33608
338			fd = do_open(fname, O_RDONLY, 0);
(gdb) STOP HERE

4. From another terminal, truncate /root/file to 0

# truncate -s 0 /root/file

5. Continue rsync process

(gdb) cont

Actual results:

send_files mapped /root/file of size 0
calling match_sums /root/file
file

Program received signal SIGSEGV, Segmentation fault.
map_ptr (map=map@entry=0x0, offset=offset@entry=2893021184, len=len@entry=32768) at fileio.c:247
247		if (offset >= map->p_offset && offset+len <= map->p_offset+map->p_len)
(gdb)

Expected results:

Not dying