Invoking the following crashes immediately with mount claiming its unable to allocate memory:
sudo mount -t overlay overlay -o lowerdir=/home/foo,upperdir=/mnt/home /home/foo
For context, /mnt/home is /dev/sda3, the 3rd partition of a flash drive formatted in ext4, /{home} is /dev/sda1, the 1st partition of the same flash drive but mounted in read-only mode because it's a live OS (booting from the flash drive).
I ran it with strace, too, and got the below
execve("/run/wrappers/bin/sudo", ["sudo", "mount", "-t", "overlay", "overlay", "-o", "lowerdir=/home/foo,upperdir=/mn"..., "/home/foo"], 0x7fff5bf43738 /* 63 vars */) = 0
access(0x7f28dafd4883, F_OK) = -1 ENOENT (No such file or directory)
brk(NULL) = 0x55d7e0d7a000
fcntl(0, F_GETFD) = 0
fcntl(1, F_GETFD) = 0
fcntl(2, F_GETFD) = 0
access(0x7f28dafd4883, F_OK) = -1 ENOENT (No such file or directory)
access(0x7f28dafd8a00, R_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, 0x7ffce760b0d0, 0x7ffce760b1b0, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, 0x7ffce760b0d0, 0x7ffce760b1b0, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, 0x7ffce760b0d0, 0x7ffce760b1b0, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, 0x7ffce760b0d0, 0x7ffce760b1b0, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, 0x7ffce760b0d0, 0x7ffce760b1b0, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, 0x7ffce760b0d0, 0x7ffce760b1b0, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, 0x7ffce760b0d0, 0x7ffce760b1b0, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, 0x7ffce760b0d0, 0x7ffce760b1b0, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(AT_FDCWD, 0x7ffce760b0d0, 0x7ffce760b1b0, 0) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, 0x7ffce760b0d0, O_RDONLY|O_CLOEXEC) = 3
read(3, 0x7ffce760b318, 832) = 832
pread64(3, 0x7ffce760ad40, 784, 64) = 784
pread64(3, 0x7ffce760ad10, 32, 848) = 32
pread64(3, 0x7ffce760acc0, 68, 880) = 68
newfstatat(3, 0x7f28dafd4b15, 0x7ffce760b1b0, AT_EMPTY_PATH) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f28dafac000
pread64(3, 0x7ffce760ae00, 784, 64) = 784
mmap(NULL, 1851728, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f28dade7000
mmap(0x7f28dae0d000, 1323008, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x26000) = 0x7f28dae0d000
mmap(0x7f28daf50000, 315392, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x169000) = 0x7f28daf50000
mmap(0x7f28daf9d000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b5000) = 0x7f28daf9d000
mmap(0x7f28dafa3000, 33104, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f28dafa3000
close(3) = 0
mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f28dade4000
arch_prctl(ARCH_SET_FS, 0x7f28dade4740) = 0
mprotect(0x7f28daf9d000, 12288, PROT_READ) = 0
mprotect(0x55d7e00ab000, 4096, PROT_READ) = 0
mprotect(0x7f28dafdd000, 8192, PROT_READ) = 0
brk(NULL) = 0x55d7e0d7a000
brk(0x55d7e0d9b000) = 0x55d7e0d9b000
readlink(0x55d7e00aa027, 0x55d7e0d7a2a0, 4096) = 38
newfstatat(AT_FDCWD, 0x55d7e0d7a2a0, 0x7ffce7609f30, AT_SYMLINK_NOFOLLOW) = 0
geteuid() = 1001
write(2, 0x7ffce7607770, 143) = 143
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f28dade3000
rt_sigprocmask(SIG_UNBLOCK, 0x7ffce7609d30, NULL, 8) = 0
rt_sigprocmask(SIG_BLOCK, 0x7ffce7609ca0, 0x7ffce7609c20, 8) = 0
getpid() = 3614
gettid() = 3614
tgkill(3614, 3614, SIGABRT) = 0
rt_sigprocmask(SIG_SETMASK, 0x7ffce7609c20, NULL, 8) = 0
--- SIGABRT {si_signo=SIGABRT, si_code=SI_TKILL, si_pid=3614, si_uid=1001} ---
+++ killed by SIGABRT (core dumped) +++
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